ANS:A - 0.8

The energy required to be supplied to a radioactive nucleus for the emission of a neutron varies depending on the specific nucleus and its energy state. However, as a general estimate, the energy typically falls within the range of a few MeV (Million electron volts). Among the options provided, 0.8 MeV and 7.8 MeV seem more realistic compared to 200 MeV and 10000 MeV, which are excessively high values. The actual energy required can vary significantly based on the specific nucleus and its decay characteristics. Without specific information about the nucleus in question, it's challenging to provide an accurate answer.