Assertion. The sum of the radii of ` Na^(+) and Cl^(-)` ions in NaCl cystal is 281 pm Hence, edge of the unit cell is 281 pm.
Reason. Edge of the unit cell is the distance between the centres of ` Na^(+) and Cl^(-)` ions touching each other.

Options

A. If both assertion and reason are true, and reason is the true explanation of the assertion.
B. If both assertion and reason are true, but reason is not the true explanation of the assertion.
C. If assertion is true , but reason is false
D. If both assertion and reason are false.

Answer

D

Explanation

Correct A . The edge of NaCl unit cell is the distance from `Na^+` to next `Na^+` ion or from `Cl^-` ion to next `Cl^-` ion.
Correct R. Edge of the unit cell of NaCl is double the distance between the centre of `Na^+` and `Cl^-` ions touching each other.