Which one of the following elements reacts with steam?

For the given figure,if the block remains in an equilibrium position,find the frictional force between the block and the wall in $N$.

If a unit vector is represented by $0.5\hat{i} - 0.8\hat{j} + c\hat{k}$,then the value of $c$ is:

If the extremities of a diagonal of a square are $(1, -2, 3)$ and $(2, -3, 5)$,then the length of its side is

In the visible region, the dispersive powers and the mean angular deviations for crown and flint glass prisms are $\omega, \omega^{\prime}$ and $d, d^{\prime}$ respectively. The condition for obtaining dispersion without deviation, when the two prisms are combined, is:

If $x = \sqrt{\frac{2+\sqrt{3}}{2-\sqrt{3}}}$,then $x^2(x-4)^2$ is equal to: