Assign oxidation number to the underlined elements in each of the following species:

NaBH₄

Let the oxidation number(O.N.) of B be ‘x’

We know that,

O.N. of Na = + 1

O.N. of H = -1

Therefore , we have,

1(+ 1) + 1(x) + 4(-1) = 0

1 + x-4 = 0

X = + 3

The O.N. of B is + 3.