When a ball is freely fallen from a given height,it bounces to $80\%$ of its original height. What fraction of its mechanical energy is lost in each bounce?

The ratio of anion radius to cation radius of a crystal is $10: 9.3$. Then,the coordination number of the cation in the crystal is

$A$ determinant is chosen at random from the set of all determinants of order $2$ with elements $0$ or $1$ only. The probability that the determinant chosen is non-zero is

$A$ force of $(3\hat i + 4\hat j)\, N$ acts on a body and displaces it by $(3\hat i + 4\hat j)\, m$. The work done by the force is ............. $J$.

Four resistors $A, B, C$ and $D$ form a Wheatstone bridge as shown in the figure. The bridge is balanced when $C = 100 \Omega$. If $A$ and $B$ are interchanged,the bridge balances for $C = 121 \Omega$. The value of $D$ is (in $\Omega$)

Hot concentrated sulphuric acid,on reaction with which one of the following elements,produces two gaseous products?