I want to ask question Iam using adsense block size of 250x250 which has advertisements for about 4 sites and i knew that the price of a click of that block is 2 cents how to know which site of the four sites in the block was clicked
There is no formula to know about low priced ads exactly. However you can use tool like adsblacklist.com to low about low paying keywords and MFA sites.
there is no way to know low paying ads. howerver there are websites that offers such information and you have to add it to the competitive ads filter on your google adsense account.