Question

Which one of the following arrangements represents the correct order of least negative to most negative electron gain enthalpy for $C,Ca,Al,F\text{and}O$?

• A. $Ca<Al<C<O<F$
• B. $Al<Ca<O<C<F$
• C. $Al<O<C<Ca<F$
• D. $C<F<O<Al<Ca$

Answer 1

The correct option is A $Ca<Al<C<O<F$

As the nuclear charge increases, the force of attraction between the nucleus and the incoming electron increases and hence the electron gain enthalpy becomes more negative.
Across the period from left to right the effective nuclear charge increases.

Thus, the correct order is,
$Ca<Al<C<O<F$

Hence, option (a) is the correct answer.