Which one of the following elements shows the maximum number of different oxidation states in its compounds?

$A$ wooden cube of side $10 \ cm$ floats at the interface between water and oil with its lower surface $3 \ cm$ below the interface. If the density of oil is $0.9 \ g \ cm^{-3}$, the mass of the wooden cube is (in $g$)

Work done in increasing the size of a soap bubble from a radius of $3\, cm$ to $5\, cm$ is nearly (Surface tension of soap solution $= 0.03\, Nm^{-1}$) (in $\pi \,mJ$)

In the circuit shown in the adjoining figure,the reading of the ammeter is ............ $A$.

Ammonia can be dried by

The inverse point of $(1,2)$ with respect to the circle $x^2+y^2-4x-6y+9=0$ is