Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A : The binding energy per nucleon is practically independent of the atomic number for nuclei of mass number in the range 30 to 170.
Reason R : Nuclear force is short ranged.
In the light of the above statements, choose the correct answer from the options given below

Assertion A: The binding energy per nucleon is practically constant (~8 MeV) for nuclei with mass numbers between 30 and 170. This is true.

Reason R: Nuclear force is short-ranged. This is true.

The reason correctly explains the assertion: because nuclear force is short-ranged, each nucleon interacts only with its nearest neighbors (not with all other nucleons). This saturation property of nuclear force leads to the binding energy being approximately proportional to the number of nucleons (i.e., BE/A ≈ constant) for medium-sized nuclei.

Both A and R are true, and R is the correct explanation of A.

This matches option 2.