Explanation

(c)
Let the first natural number be $x$
According to the question,
$x + x + 1 + x + 2 + x + 3 + x + 4 + x + 5 + x$
$+ 6 + x + 7 + x + 8 + x + 9 + x + 10 = 2761$
$\Rightarrow \ \ \ 11x + 55 = 2761$
$\Rightarrow \ \ \ x = \frac{2761 - 55}{11} = 246$
$\therefore$ Middle number $= x + 5 = 246 + 5 = 251$