Metastable state in laser is the intermediate state between the e2 and e1 where the excited electron can stay for a comparably long time.

Only gamma, it is the process by which a metastable excited nuclear isomer of an isotope relaxes down to the ground state of the same isotope. Some metastable states must undergo multiple gamma decays through less excited metastable states to reach the ground state.

because according to energy profile,metastable state is lying lower than excited state.as we know that states of lower energies are more stable than states of higher energy.so it is more stable than excited state.

when we provide two input as 1 or true or high out put of q and q' become same

that violate the complement law.

Excited state of an atom, nucleus, or other system that has a longer lifetime than the ordinary excited states and generally has a shorter lifetime than the ground state. It can be considered a temporary energy trap or a somewhat stable intermediate stage of a system of which the energy may be lost in discrete amounts. The many photochemical reactions of mercury are a result of the metastable state of mercury atoms, and radiation from metastable oxygen atoms accounts for the characteristic green colour of the aurora borealis and aurora australis.