Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	Generally, ionisation enthalpy increases from left to right in a period.
Reason (R):	When successive electrons are added to the orbitals in the same principal quantum level, the shielding effect of inner core of electrons does not increase very much to compensate for the increased attraction of the electron to the nucleus.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Assertion and reason both are correct statements and reason is correct explanation of assertion.

Ionisation enthalpy increases along a period because effective nuclear charge increases and atomic size decreases.