Capitial gain

Sir,

"A" was selling one housing board allotmnet house to "B" ..after some years "C" (who is the son of "A"), got that house property bond from the Government and the bond is belongs to in the name of "A".... Now "B" decide to sell that house by the way of "C"..my doubt is Who will be the liable for capital gain tax.   "B" or "C"....now "A" was no more.

What is the tax rate slab? if any way to avail exemption to avoid the tax for "A"