Which of the following mixtures can form an alloy?

Find the correct order of the given elements with respect to their size.

Iron loses its magnetic property at:

The maximum and minimum melting points of the first and second transition series elements,respectively,are obtained with $-$

The magnetic moment of a transition metal compound has been calculated to be $3.87 \ B.M.$ The metal ion is

Assertion $(A)$: $Mo$ has the ground state electronic configuration $4d^5 5s^1$.
Reason $(R)$: $Mo$ has the highest exchange energy among the second row transition elements.
The correct option among the following is: