Read the given expression.
x = atomic number − number of core electrons
which of the following explains the identity of x and its trends down a group?
a). x is the effective nuclear charge, and it remains constant down a group.
b). x is the screening constant, and it remains constant down a group.
c). x is the effective nuclear charge, and it increases down a group.
d). x is the screening constant, and it increases down a group.