Question

Assertion(A) : The unit based for measuring nuclear cross-section is 'barn'
Reason(R) : 1barn= 10^-28m^2​

Answer 1

$\mathfrak{\huge{\pink{\underline{\underline{AnSwEr:-}}}}}$

Actually Welcome to the Concept of the Nuclear Physics.

Here, we can see that, Both the Assertion and reason are correct, such that, "Barn" is the unit of Nuclear cross-section and also the other universal fact that

1 barn = 10^-28 m^2 , are true, but the second statement is proved fact by calculations and does not clearly supports the first statement.

Thus, Option 2.) is the Answer.

==> Both Assertion and Reason are correct but reason is not the correct explanation of assertion.