Assertion (A):	A black body is an ideal body that emits and absorbs radiation of all frequencies.
Reason (R):	The frequency of radiation emitted by a body goes from lower frequency to a higher frequency with an increase in temperature.

  

1.	Both (A) and (R) are True and (R) is the correct explanation of (A).
2.	Both (A) and (R) are True but (R) is not the correct explanation of (A).
3.	(A) is True but (R) is False.
4.	(A) is False but (R) is True.

$1.$ $6.023$ $\times$ ${10}^{23}$
$2.$ $6.023$ $\times$ ${10}^{24}$
$3.$ $6.023$ $\times$ ${10}^{22}$
$4.$ $1.619\times$ ${10}^{23}$

The total number and mass of neutrons in 7 mg of ¹⁴C would be :

(Assume that mass of a neutron = 1.675 × 10^–27 kg)

\(1 .\) \(2 . 41\) \(\times\) \(\left(10\right)^{21}\) \(,\) \(4 . 03\) \(\times\) \(\left(10\right)^{– 6}\) \(kg\)
\(2 .\) \(6 . 23\) \(\times\) \(\left(10\right)^{23}\) \(,\) \(1 . 67\) \(\times\) \(\left(10\right)^{- 21} kg\)
\(3 .\) \(1 . 22\) \(\times\) \(\left(10\right)^{22}\) \(,\) \(4 . 03\) \(\times\) \(\left(10\right)^{6}\) \(kg\)
\(4 .  2 . 41\) \(\times\) \(\left(10\right)^{21}\) \(,\) \(4 . 03\) \(\times\) \(\left(10\right)^{- 6}\) \(g\)

The wave number of a light whose time period is 2.0 × 10^–10 s would be:

1. 16.66 m^–1

2. 1.66 m^–1

3. 32.34 m^–1

4. 12.34 m^–1

The number of photons of light with a wavelength of 4000 pm that provide 1J of energy would be: 

$1.$ $2.01$ $\times$ ${10}^{16}$
$2.$ $2.01$ $\times$ ${10}^{19}$
$3.$ $4.14$ $\times$ ${10}^{23}$
$4.$ $2.14$ $\times$ ${10}^{21}$

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise sodium atom. The ionisation energy of sodium in kJ mol^–1 is :

1. 494

2. 4.94

3. 516

4. 0.50

A 25-watt bulb emits monochromatic yellow light with a wave length of 0.57µm. The rate of emission of quanta per second would be :

1. 7.17 × 10^–19 s^–1

2. 4.13 × 10¹⁶ s^–1

3 . 7.17 × 10¹⁹ s^–1

4 . 1.26 × 10²⁰ s^–1
${\mathrm{}}^{}$

The wavelength of light emitted when the electron in a H atom undergoes the transition from an energy level with n = 4 to an energy level with n = 2, is :

1. 586 mm

2. 486 nm

3. 523 nm

4. 416 pm

The energy associated with the fifth orbit of a hydrogen atom is :

$1.$ $-2.18$ $\times$ ${10}^{-18}$ $\mathrm{J}$
$2.$ $-8.72$ $\times$ ${10}^{-20}$ $\mathrm{J}$
$3.$ $-3.88$ $\times$ ${10}^{-21}$ $\mathrm{J}$
$4.$ $-8.72$ $\times$ ${10}^{-19}$ $\mathrm{J}$