Question

The first ionisation enthalpy of the elements are in the order of:

• A. $C<Si<N<P$
• B. $N<Si<C<P$
• C. $Si<N<C<P$
• D. none of the above

Answer 1

The correct option is D none of the above

The IE increases in a period as the size decreases from left to right.

thus IE of $C<N$ and $Si<P$

As we move down the group the size increases and thus IE decreases.

$\therefore$ IE $Si<C$ and $P<N$

on rearranging them we get:

$Si<P<C<N$