What is the representation of an element having mass number of 40 and 21 neutrons in it?

Which of the following orbitals have same value of $(\mathrm{n}+l)$ as that of 3 d orbital?

What is momentum of a microscopic particle having de Broglie's wavelength 6.0 A?

$$\left(\mathrm{h}=6.63 \times 10^{-34} \mathrm{Js}\right)$$

What is energy associated with fourth orbit of hydrogen atom?

$$\left(\mathrm{R}_{\mathrm{H}}=2.18 \times 10^{-18} \mathrm{~J}\right)$$