Cobalt $(III)$ chloride forms several octahedral complexes with ammonia. Which of the following will not give a test for chloride ions with silver nitrate at $25\,^{\circ}C$?

Which of the following pairs contains structurally similar substances?

In the diagram,the input is across the terminals $A$ and $C$ and the output is across the terminals $B$ and $D$. Then the output is

The random variable $X$ takes the values $1, 2, 3, \ldots, m$. If $P(X=n) = \frac{1}{m}$ for each $n$,then the variance of $X$ is

Two metal plates each of area $A$ form a parallel plate capacitor with air in between the plates. The distance between the plates is $d$. $A$ metal plate of thickness $d/2$ and of same area $A$ is inserted between the plates to form two capacitors of capacitances $C_1$ and $C_2$ as shown in the figure. If the effective capacitance of the two capacitors is $C^{\prime}$ and the capacitance of the capacitor initially is $C$,then $C^{\prime}/C$ is

The cause of water pollution is due to