In the following pairs,the one in which both transition metal ions are colourless is

When light of wavelength $\lambda$ is incident on a photosensitive surface,the stopping potential is $V$. When light of wavelength $3 \lambda$ is incident on the same surface,the stopping potential is $\frac{V}{6}$. The threshold wavelength for the surface is:

Two capacitors $C_1$ and $C_2$ are charged to $120 \ V$ and $200 \ V$ respectively. It is found that by connecting them together,the potential on each can be made zero. Then:

The following series $L-C-R$ circuit,when driven by an emf source of angular frequency $70 \text{ krad/s}$,the circuit effectively behaves like:

If the charge on a capacitor is increased by $2 \, C$,the energy stored in it increases by $21 \%$. The original charge on the capacitor (in coulomb) is

If the pressure at half the depth of a lake is equal to $2/3$ of the pressure at the bottom of the lake,then what is the depth of the lake in $m$? (Assume atmospheric pressure $P_0 = 10^5 \ Pa$,density of water $\rho = 10^3 \ kg/m^3$,and $g = 10 \ m/s^2$)