Heavy nuclides with too few neutrons to be in the band of stability are most likely to decay by what mode?

Positron emission

Explanation:

Positron emission involves the conversion of a proton to a neutron. This process increases the mass number of the daughter nucleus by 1 while its atomic number remains the same. The new neutron increases the number of neutrons present in the daughter nucleus hence the process increases the N/P ratio.

A positron is usually ejected in the process together with an anti-neutrino to balance the spins.

your answer is a. the enthalpy of formation for a pure element in its standard state is always positive.