Sec 54 of i.t act

exemption u/s 54 can be claimed only in respect of  one house.  So in your case as CG on the house sold in Apr12 is more than the house sold in Mar12, so you can claim the exemption for house two against eh house purchased in Dec11 for Rs. 60lacs.  In this way you can save the entire Cg of Rs. 40clas.  for the house sold in Mar12 you can claim the exemption u/s 54EC by investing the Cg under the bonds issued by NHAI or REC.  As the limit in these bonds to invest is maximum upto 50lacs & your CG is coming only upto 10lcas you can invest the entire CG in the bonds u/s 54EC.  however you will ahve to make the investments within 6months from the date of transfer.

Under section 54 of the income tax act 1961, if the new house property procured is one year before the date of transfer or two years after the date of transfer, then such property becomes eligible for deduction . In the above case Sale of P1 - Rs.10L (procured in the year  March-2012) & P2 - Rs.40L (in the year  April-2012). Propert procured - 60L(Dec-2011), since property is procured one year before the date of transfer it is eligible. The maximum amount eligible is value of capital gain or value of property  whichever is lesser.

The expression"a residential house" is used in section 54, so which would mean any number of house sold is eligible for deduction because of the following :

The article "a" is not necessarily a singular item. It is often used in the sense of any, & when so used it may be applied to more than one individual object - National Union Bank v.Copeland

Moreover clarification by Board vide letter No.247/24/76-IT (A-II), dated March 25 1977 would further strengthen this view,

"assessee retained more than one house for the purpose of his own or parents' own residence & has used them for such residence from time to time, whether capital gain arising on transfer of each of such houses should qualify or exemption"