When a metal surface is irradiated with light of frequency $x \mathrm{~Hz}$, the kinetic energy of emitted photoelectrons is $z \mathrm{~J}$. When the same metal is irradiated with light of frequency $y \mathrm{~Hz}$, the kinetic energy of emitted electrons is $z / 3 \mathrm{~J}$. What is threshold frequency (in Hz ) of metal?

Identify the correct statements from the following

I. Isotopes of an element show different chemical behaviour.

II. Lyman series of lines of hydrogen spectrum appear in UV region.

III. The oscillating electric and magnetic field components of electromagnetic radiation are perpendicular to each other and both are perpendicular to the direction of propagation of radiation.

The sum of number of angular nodes and radial nodes for $4 d$-orbital is

If the position of the electron was measured with an accuracy of +0.002 nm . The uncertainty in the momentum of it would be (in $\mathrm{kg} \mathrm{ms}^{-1}$ )

$$ \left(h=6.626 \times 10^{-34} \mathrm{Js}\right) $$