electron configuration assignment\nthe rule for the d - block is...\no $n - 3$\no $n - 2$\no $n - 1$

Brief Explanations:

In electron - configuration, for the d - block elements, the principal quantum number of the d - orbital is (n - 1), where (n) is the principal quantum number of the outermost s - orbital. For example, in the fourth period ((n = 4)), the transition metals have electrons filling the 3d orbitals ((n-1 = 3) when (n = 4)).

Answer:

(n - 1)