Which metal does not react with cold water but releases $H_2$ gas upon reacting with steam?

When a capacitor is connected in series to an $LR$ circuit,the alternating current flowing in the circuit

In a $\triangle ABC$,if $a \cos^2 \frac{C}{2} + c \cos^2 \frac{A}{2} = \frac{3b}{2}$,then the sides of the triangle are in

If $k > 1$ and the determinant of the matrix $A^2$,where $A = \begin{bmatrix} k & k\alpha & \alpha \\ 0 & \alpha & k\alpha \\ 0 & 0 & k \end{bmatrix}$,is $k^2$,then $|\alpha|$ is equal to

If the area bounded by $y = ax^2$ and $x = ay^2$ for $a > 0$ is $1$,then $a =$

The value of $x$,where $x>0$ and $\tan \left(\sec ^{-1}\left(\frac{1}{x}\right)\right)=\sin \left(\tan ^{-1} 2\right)$ is