If frequency of the X-rays produced using an element as anti-cathode is found to be 2500 sec^-1, the atomic number of used element is (a, b= 1)

1. 51

2. 49

3. 56

4. 72

What is the energy required per mole to excite an electron from the third to fifth Bohr orbit in hydrogen ?

1. 6.336 x 10⁶J

2. 7.122 x 10⁴J

3. 0.343 x 10⁶J

4. 9.343 x 10⁴J

The energy of electron in first Bohr's orbit of H-atom is -13.6 eV. What will be its potential energy in n = 4.

1. –13.6 eV

2. - 3.4 eV

3. -0.85 eV

4. -1.70 eV

Sodium atoms can be ionised by supplying an energy of 118 kcal mol^-1. Using this data, calculate the lowest possible frequency of light that can ionise a sodium atom.

(h = 6.624 x 10^-27 erg.sec, c= 3 x 10¹⁰ cm sec^-1).

1. 1.24 x 10¹⁵ sec^-1

2. 0.24 x 10¹⁵ sec^-1 

3. 12.4 x 10¹² sec^-1

4. 2.31 x 10¹⁸ sec^-1

A glow worm of mass 5.0 g emits red light (650 nm) with a power of 0.1 W. entirely in the backward direction. What velocity would it accelerate to after 10 years, if released in free space (and assumed to be alive)?

1. 9.14 ms^-1 

2. 28.08 ms^-1

3. 11.05 ms^-1

4. 21.04 ms^-1

Which of the following postulates does not belong to Bohr's model of the atom?

1. Angular momentum is an integral multiple of h/2$\mathrm{\pi }$

2. The electron stationed in the orbit is stable

3. The path of an electron is circular

4. The change in the energy levels of electron is continuous

The total number of orbitals having l = 3  is - 

1. 3

2. 7

3. 5

4. 9

Bohr's atomic model provides explanations for:

The presence of one electron each in the three 2p sub-shell of nitrogen is explained by 

1. Uncertainty principle

2. Hund's rule

3. Pauli's principle 

4. Bohr's theory

When the atoms of gold sheet are bombarded with a beam of $\alpha$ -particles, only a few a-particles get deflected where as most of them go straight undeflected. This is because: