The operation of a nuclear reactor is said to be critical when the value of the neutron multiplication factor $K$ is:

If $\cos ^{-1}\left(\frac{5}{13}\right)+\cos ^{-1}\left(\frac{3}{5}\right)=\cos ^{-1} x$,then $x$ is equal to

The focus of the parabola $y = 2x^2 + x$ is

Maximum bond angle is present in

$\cos A \cos 2 A \cos 4 A \ldots \cos 2^{n-1} A$ equals

An aqueous solution of $6.3 \ g$ of oxalic acid dihydrate is made up to $250 \ mL$. The volume of $0.1 \ N \ NaOH$ required to completely neutralize $10 \ mL$ of this solution is ............. $mL$.