(d)
$\lim_{x \rightarrow 0}\frac{2^{x} - 2^{- x}}{x} = \lim_{x \rightarrow 0}\ 2^{x}\log{2 + 2^{- x}\log 2}$
[by L’ Hospital’s rule]
$= \log 4$
Since, the function is continuous at $x = 0$
$\therefore\ \ \ \ \ \ f(0) = \lim_{x \rightarrow 0}\ f(x)\ \ \Rightarrow \ \ \ \ f(0) = \log 4$