Long Term Capital Gain from sale of Mutual Funds

Sir,

What are pre-conditions for claiming exemption from Long term capital gain on Sale of Mutual Funds.

Please clarify whether one has to reivest the entire  sale proceeds to claim exemption.

Can we claim exemption up to Rs.100000/- with out further investments. if so, under which section.

Please reply at the earliest.

Thanks & regards,

Gopalakrishna Pillai