Explanation

(c)
A man has two options for every friend either they invited it or not.
$\therefore$ Required number of ways $= 2^{7} - 1 = 127$
[Since, we have to subtract those cases in which he does not invite any friend $ie$, $\ ^{n}C_{0} = 1\rbrack$
Alternate Solution
Required number of ways $= \ ^{7}C_{1} + \ ^{7}C_{2} + \ ^{7}C_{3} + \ldots + \ ^{7}C_{7}$
$= 2^{7} - 1$