OM PRAKASH, J. - (1.) Writ Petition Nos. 645 of 1994, 872 of 1994 and 68 of 1995 though argued by different counsel and the other connected writ petitions enumerated in the schedule to this judgment, in which none has appeared for the petitioners to argue, give rise to common questions and therefore, they are being disposed of by a common judgment. First, we take up the leading Writ Petition No. 645 of 1994 with which all other petitions were connected. This petition has been argued by Sri Bharat Ji Agarwal for the petitioners and undisputed facts are that the petitioner No. 1, a company incorporated under the Indian Companies Act, 1956, is engaged in the manufacture of notified goods, namely, "menthol", for which raw material is "mentha oil". By notification dated August 29, 1987, issued in exercise of the powers under section 4-B of the Uttar Pradesh Sales Tax Act, 1948 (briefly, "the Act"), read with section 21 of the Uttar Pradesh General Clauses Act, 1904 (for short, "the General Clauses Act") purchases of raw material, which is mentha oil, as aforesaid, in this case, were fully exempted. By the impugned notification dated May 21, 1994 (annexure "2" to the writ petition) issued under section 4-B of the Act, read with section 21 of the General Clauses Act, purchase tax was levied at the rate of 2 per cent on the sales as well as purchases and, therefore, the petitioner, admittedly - a purchasing dealer - became liable to pay purchase tax at the rate of 2 per cent on the purchases of the raw material, i. e. , mentha oil, used for the manufacture of the notified goods, i. e. , menthol, as mentioned at serial No. 2 of annexure II to the notification dated August 29, 1987. The notification dated August 29, 1987, when properly read, states that in supersession of all the previous notifications issued under section 4-B of the Act, the Governor is pleased : (a) to declare the goods mentioned in column 2 of annexures I, II and III to this notification to be notified goods for the purposes of the aforesaid section 4-B, and (b ). . . . . . . . . . . . . . . . . . . . (1 ). . . . . . . . . . . . . . . . . . . . (2) No tax shall be payable in respect of the sale to or, as the case may be, purchase by a dealer, holding a recognition certificate as aforesaid, of goods mentioned in column 3 of annexure II required for use as raw material in the manufacture by him of the notified goods mentioned in column 2 of the said annexure. The petitioner, admittedly, holds a recognition certificate (annexure "3" to the writ petition), which was granted to the petitioner with effect from March 18, 1987 initially for the years from 1987-88 to 1989-90. Later, that was renewed up to March 31, 1996. In this recognition certificate it was mentioned that purchases of mentha oil used for the manufacture of menthol, were fully exempt. The contention of Shri Bharat Ji Agarwal, is that when purchases of mentha oil were fully exempt under the recognition certificate renewed up to the year 1995-96, the impugned notification dated May 21, 1994 (annexure "2" to the writ petition) could not have been issued by respondent No. 1 making the petitioner liable to pay tax at the rate of 2 per cent on the purchases of raw material. It is contended by him that unless the recognition certificate is amended under sub-section (4) of section 4-B of the Act, respondent No. 1 is not empowered to cut down the period of exemption and impose tax at the rate of 2 per cent on the purchases till the end of the year 1995-96 up to which the recognition certificate was issued. Learned counsel for the petitioner submits that full exemption on the purchases of raw material was granted to the petitioner under the recognition certificate up to the end of the year 1995-96 and that right having been vested in the petitioner by virtue of the recognition certificate, cannot be taken away by the respondents, unless the recognition certificate itself is legally amended under sub-section (4) of section 4-B of the Act. On these premises, the petitioners have challenged the validity of the impugned notification dated May 21, 1994 (annexure "2" to the writ petition ). We do not see any force in the submission of the petitioner's counsel that no tax can be imposed by the impugned notification. We do not agree with the submission of Sri Bharat Ji Agarwal, that full exemption on purchases was granted under the recognition certificate and that the exemption so granted was co-extensive and co-terminous with the recognition certificate. So long as the recognition certificate remains effective, full exemption granted under the notification of August 29, 1987, will continue, says Shri Bharat Ji Agarwal. The question for consideration is whether exemption was granted under the recognition certificate. Sub-section (2) of section 4-B, briefly, states that where a dealer requires any goods referred to in sub-section (1) for use in the manufacture by him, in the State of any notified goods, such notified goods manufactured or possessed by him, and such notified goods are intended to be sold by him in the State or in the course of inter-State trade, etc. , he may apply to the assessing authority in such form and manner and within such period as may be prescribed for the grant of a recognition certificate in respect thereof and if the applicant satisfies such requirements and conditions as may be prescribed, the assessing authority shall grant to him in respect of such goods a recognition certificate in such form and subject to such conditions as may be prescribed. Clause (b) to the second proviso to clause (a1) of sub-section (1) of section 4-B, pithily state that where any goods liable to tax under any other provision of this Act are sold by a dealer to another dealer and such other dealer furnishes to the selling dealer a recognition certificate issued under sub-section (2) in respect thereof, the selling dealer shall be liable in respect of those goods to tax at such concessional rate or be wholly or partly exempt from tax, whether unconditionally or subject to the conditions as specified in that behalf as may be notified in the gazette by the State Government in that behalf. It is clear from clause (b) to the second proviso that if a purchasing dealer furnishes a recognition certificate to the selling dealer, then the selling dealer shall be liable in respect of those goods to tax either on concessional rates or wholly or partly exempt from tax as notified in the gazette by the State Government in that behalf. Therefore, a purchasing dealer holding a recognition certificate will be entitled to exemption either wholly or partly as may be notified in the Gazette by the State Government. Concessional rate or exemption either wholly or partly is available only to a dealer, who holds a recognition certificate and not to any one else, but it is clear that exemption wholly or partly does not flow from the recognition certificate but from the notification published in the gazette by the State Government in that behalf. Sub-section (1) of section 4-B beginning with the non obstante clause in so far as material, states that notwithstanding anything contained in sections 3, 3-A, 3-AAAA and 3-D, where any goods liable to tax under sub-section (1) of section 3-D are purchased by a dealer who is liable to tax on the turnover of first purchases under that sub-section and the dealer holds a recognition certificate issued under sub-section (2) in respect thereof, he shall be liable in respect of those goods to tax at such concessional rate, or be wholly or partly exempt from tax, whether unconditionally or subject to the conditions and restrictions specified in that behalf, as may be notified in the gazette by the State Government in that behalf. From clause (a) of sub-section (1) of section 4-B, it is manifest that a purchasing dealer liable to tax under sub-section (1) of section 3-D, will be entitled to exemption either wholly or partly as may be notified in the gazette by the State Government, provided he has a recognition certificate. Recognition certificate is merely a pre-requisite condition to qualify for exemption either wholly or partly, but the exemption is not founded in the recognition certificate. It is true that unless a purchasing dealer liable to tax under sub-section (1) of section 3-D, holds a recognition certificate, no exemption either wholly or partly can be granted to him. A purchasing dealer may qualify to get exemption under the notification published in the gazette by the State Government, but the exemption is granted by the notification issued under sub-section (1) of section 4-B in that behalf. The exemption - either whole or part - not being emanating from the recognition certificate, but from the notification, published in the Gazette by the State Government, the submission of Sri Bharat Ji Agarwal that unless the recognition certificate is legally amended under sub-section (4) of section 4-B, full exemption granted to the petitioner cannot be taken away by respondent No. 1 by the impugned notification (annexure "2" to the writ petition), has to be rejected. Sri Bharat Ji Agarwal lost sight of the fact that exemption was granted to the petitioner by the notification of August 29, 1987, and not by the recognition certificate (annexure "3" to the writ petition ). The recognition certificate not being the source of exemption, but merely one of the conditions to be fulfilled for qualifying for exemption, no amendment as a matter of fact, is needed in the recognition certificate. Once the notification of August 29, 1987, giving exemption to the petitioner is superseded by another notification, the petitioner will lose the exemption at once, unless another notification giving full exemption is issued. Respondent No. 1 herein issued the impugned notification dated May 21, 1994 (annexure "2" to the writ petition) making the petitioners liable to pay tax at the rate of 2 per cent on the purchases of raw material used in the manufacture of notified goods. Therefore, the right to claim full exemption extinguished and liability to pay tax at the rate of 2 per cent on purchases of raw material was created by the impugned notification (annexure "2" to the writ petition ). This can be legally done by the State Government under section 4-B, read with section 21 of the General Clauses Act. Section 21 of the General Clauses Act declares that where by any Uttar Pradesh Act, a power to issue statutory instruments is conferred, then that power includes a power exercisable in the like manner and subject to the like sanctioned and conditions, if any, to add, amend, vary or rescind in statutory instruments so issued. Amply conferred power under section 21 of the General Clauses Act enables the State Government to rescind or supersede a notification earlier issued under clause (a) of sub-section (1) of section 4-B. In Shri Bakul Oil Industries v. State of Gujarat [1987] 64 STC 304 (SC); AIR 1987 SC 142, it was ruled down that if exemption granted by the Government was only by way of concession, it was always open to the State Government to withdraw or revoke the concession. However, the Supreme Court observed that the power of revocation or withdrawal would be subject to one limitation, viz. , the power cannot be exercised in violation of the rule of promissory estoppel. The principle of promissory estoppel has not been pressed before us in the writ petition argued by Sri Bharat Ji Agarwal. In the case in hand, it is no doubt clear that the exemption was granted as a matter of concession. But for the notification dated August 29, 1987, the petitioner would have been liable to pay tax on purchases under sub-section (1) of section 3-D. Clause (b) to the second proviso to clause (a1) of sub-section (1) of section 4-B merely carves out an exception, in that if a recognition certificate is furnished by a purchasing dealer to the selling dealer, then the latter shall be liable in respect of those goods to tax either at concessional rate or wholly or partly exempt from tax as may be notified in the Gazette by the State Government. By clause (b), liability to tax the purchases under sub-section (1) of section 3-D was shifted to the selling dealer, provided a recognition certificate is furnished by the purchasing dealer to the selling dealer, but by the impugned notification with a view to rationalising the tax liability, as contended by learned Additional Advocate-General, the liability to tax on purchases is again fastened on the purchasing dealer at the rate of 2 per cent. From annexure III to the notification dated August 29, 1987, it is clear that the purchases of raw material as mentioned in column 3 of the annexure II to the notification were fully exempt, but the purchases of raw materials mentioned in column 3 of annexure III to the notification, rate of tax varied from 2 per cent to 4 per cent. To rationalise the tax liability on the raw materials used for the manufacture of notified goods at the uniform rate of 2 per cent respondent No. 2 issued the impugned notification. Rationalization or simplification of tax liability cannot be said to be contrary to the public interest. Full exemption on the purchases liable to tax under sub-section (1) of section 3-D being only a concession, could be revoked or withdrawn by respondent No. 1 at any time and this is what precisely has been done by respondent No. 1 by the impugned notification in the public interest. In the matter of taxation laws, the Legislature enjoys greater latitude as regards classification, choice of persons and the article to be taxed, fixation of rate of tax, etc. , and its choice is normally respected by the courts. Exemption implies that purchases are liable to tax and, therefore, the exemption cannot be claimed by the petitioner as a matter of right, but that would be available to the petitioner so long as the notification dated August 29, 1987, remained operative. For the reasons, we uphold the validity of the impugned notification dated May 21, 1994 (annexure "2" to the writ petition ). Only up to that date, the petitioners will be entitled to full exemption and for future they will be liable to pay tax at 2 per cent on the purchases of specified raw material being used in the manufacture of the notified goods. Such liability can again be varied by respondent No. 1 by issuing a fresh notification in supersession of the impugned notification. Writ Petition No. 872 of 1994 : Sri Rakesh Ranjan, appearing in the Writ Petition No. 872 of 1994 has adopted the arguments advanced by Sri Bharat Ji Agarwal fully. The only factual change between Writ Petition No. 872 of 1994 and Writ Petition No. 645 of 1994 is that in the former the raw material is paddy, in the latter the raw material is mentha oil. Legal position will, however, remain the same, as both mentha oil and paddy are mentioned in column 3 of annexure II to the notification dated August 29, 1987, at serial Nos. 2 and 3 respectively. Writ Petition No. 68 of 1995 : Turning to the arguments of Sri Sunil Ambwani, appearing in Writ Petition No. 68 of 1995, we reject his contention that the impugned notification is violative of the doctrine of promissory estoppel. In the notification dated August 29, 1987, no period of full exemption is stated. Also there is nothing to indicate that the petitioner acted to its detriment pursuant to any promise held out by respondent No. 1 and, therefore, the doctrine of promissory estoppel cannot be pressed into service. Rest of the submissions of Sri Ambwani are similar to those advanced by Sri Bharat Ji Agarwal and, therefore, our view remains the same that we have taken in Writ Petition No. 645 of 1994. In the writ petitions enumerated in the Schedule same question is involved. For the reasons, all the writ petitions fail and are dismissed. Interim orders passed in all the writ petitions are hereby vacated. Writ petitions dismissed. .;