Ppf: deposits per month

there is no such requirement under the PPF Act, that a particular amount shud be deposited in the account each month.  You can deposit any amount you want each month or anytime during the year, but deduction u/s 80C wud be restricted only upto Rs 1lacs.  also you will have to deposit minium 500Rs for the year, otherwise  you would have to pay penalty charges for keeping the account active.

Dear Sirs,

My query is whether we can deposit two or more instalments in one month only. I deposited two instalments in one month only, that is, April, 2012.  In any case my total instalments will not exceed 12 in the whole year. Is it okay if I made two subscripttions in one month only? Kindly address this particular doubt. 

Yes you can do that, no issues with it.