Explanation

(c) The number of fringes on either side of centre C of screen is
$n_{1} = \left\lbrack \frac{AC}{\beta} \right\rbrack = \left\lbrack \frac{0.5}{0.021} \right\rbrack = \lbrack 23.8\rbrack = 23$
$\therefore$ Total number of fringes
$= 2n_{1} + fringe\ at\ centre$
$= 2n_{1} + 1 = 2 \times 23 + 1$
$= 46 + 1 = 47$
In Young’s experiment, the number of fringes should be odd.