283Electron affinity is the energy release in adding up an electron to a neutral atom in its gaseous state to form an negative ion.
X(g) + e- → X- + Energy(E.A)
E.A increase across the period as non metal have high E.A a metal.( Since metallic character decrease across the period so E.A increase across period.
E.A decrease down the group because metallic characters increase down the group.