The orbital angular momentum of an electron in 2s orbital is

• $+\frac{1}{2}\frac{\mathrm{h}}{2\mathrm{\pi }}$

• zero

• $\frac{\mathrm{h}}{2\mathrm{\pi }}$

• $\sqrt{2}\frac{\mathrm{h}}{2\mathrm{\pi }}$

The number of electron and neturons of an element is 18 and 20 respectively. Its mass number is

• 2

• 17

• 37

• 38

$\mathrm{The} \mathrm{number} \mathrm{of} \mathrm{\alpha } \mathrm{and} \mathrm{\beta } \mathrm{particles} \mathrm{emitted} \mathrm{in} \mathrm{nuclear} \mathrm{reaction} {}_{90}\mathrm{Th}^{228}\to {}_{83}\mathrm{Bi}^{212}$ are respectively

• 4,1

• 3,7

• 8,1

• 4,7

The radius of hydrogen atom is 0.53 Å. The radius of ₃Li²⁺ is of:

• 1.27 Å

• 0.17 Å

• 0.57 Å

• 0.99 Å

Wave nature of electrons was demonstrated by :

• Schrodinger

• de-Broglie

• Davisson and Garmer

• Heisenberg

4d, 5p, 5f and 6p orbitals are arranged in the order of decreasing energy. The correct option is:

• 6p > 5f > 5p > 4d

• 6p > 5f > 4d > 5p

• 5f > 6p > 4d > 5p

• 5f > 6p > 5p > 4d

Which of the following series of transitions in the spectrum of hydrogen atom fall in visible region?

• Balmer series

• Paschen series

• Brackett series

• Lyman series

Non - directional orbital is :

• 4p

• 4d

• 4f

• 3s

Assertion (A) : Atoms with completely filled and half-filled sub-shells are stable.

Reason (R): Completely filled and half-filled sub-shells have symmetrical distribution of electrons and have maximum exchange energy.

The correct answer is

• (A) and (R) are correct, (R) is the correct explanation of (A)

• (A) and (R) are correct, (R) is not the correct explanation of (A)

• (A) is correct, but (R)is not correct

• (A) is not correct, but (R) is correct