Question

Which of the following set represents the correct order of first ionization potential?

• A. K>Na>Li
• B. Be>Mg>Ca
• C. B>C>N
• D. Ge>Si>C

Answer 1

The correct option is B

Be>Mg>Ca

Down the group ionization enthalpy decreases with an increase in atomic size. Along the period it increases due to an increase in effective nuclear charge and decrease in size.
K > Na > Li ---> same group, going upwards ---> ionization potential decreases.
Be > Mg > Ca ----> same group but going downwards ---> ionization potential increases.
B > C > N ---> same period, going left to right --->ionization potential increases.
Ge > Si > C ----> same group, going upwards. --->ionization potential decreases.