Question

How to solve Q-15 pls tell

Answer 1

option NO. B WILL TURN OUT TO BE THE CORRECT OPTION , AS WHEN U WILL SEE THE TREND IN IONISATION ENTHALPY , THEN in that case first it will increase upto the middle then become constant and then it will decrease .. 
but as per your given table its constantly increaseing but last 2 I.E are increaseing very rapidly . 
so. it will be obviously silicon as when u will remove the 2 valence or outer shell electron it will be make almost stable and stable config. will be prferrable by almost all element . 
HOPE IT CLEARS YOUR DOUBT