The set representing the correct order of the first ionisation potential is

Options

A. `K gt Na gt Li`
B. `Be gt Mg gt ca`
C. `B gt C gt N`
D. `Ge gt Si gt C`

Answer

B

Explanation

Down the group the effective nuclear charge remains almost constant. But down the group with increasing atomic number, the number of shells increase and thereby atomic size increase. As a result, the distance of valence shell electron from nucleus increases, attraction between them decreases and therefore ionization energy decreases.