In the concentration of $PbS$ containing $ZnS$ as impurity,the depressant used is:

Which of the following series of transition metal ions all have a $3d^2$ electronic configuration?

If $f(x) = \int \frac{5x^8 + 7x^6}{(x^2 + 1 + 2x^7)^2} dx, (x \ge 0)$ and $f(0) = 0$,then the value of $f(1)$ is

The efficiency of a Carnot engine is $50\%$ and the temperature of the sink is $500\, K$. If the temperature of the source is kept constant and its efficiency is to be raised to $60\%$,then the required temperature of the sink will be........ $K$.

$A$ convex lens is made up of three different materials as shown in the figure. For a point object placed on its axis,the number of images formed are

Which of the following compounds forms silicones on hydrolysis?