# The number of photons of light with a wavelength of 4000 pm that provide 1J of energy would be:  $1.$ $2.01$ $×$ ${10}^{16}$$2.$ $2.01$ $×$ ${10}^{19}$$3.$ $4.14$ $×$ ${10}^{23}$$4.$ $2.14$ $×$ ${10}^{21}$

Subtopic:  Planck's Theory |
68%
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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

Subtopic:  Planck's Theory |
From NCERT
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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. 4.13×1016s-1

3 . 7.17×1019 s-1

4 . 1.26 ×1020s-1
${}^{}$

Subtopic:  Planck's Theory |
66%
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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

Subtopic:  Hydrogen Spectra |
67%
From NCERT
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The energy associated with the fifth orbit of a hydrogen atom is :

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

Subtopic:  Hydrogen Spectra |
70%
From NCERT
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The wave number for the longest wavelength transition in the Balmer series of atomic hydrogen would be -
1. $$1 . 1 . 52 \times \left(10\right)^{6} m^{- 1}$$
2. $$2 . 3 . 14 \times \left(10\right)^{6} \left(cm\right)^{- 1}$$
3. $$3 . 15 . 2 \times \left(10\right)^{6} m^{- 1}$$
4. $$4 . 1 . 52 \times \left(10\right)^{6} \left(cm\right)^{- 1}$$

Subtopic:  Hydrogen Spectra |
60%
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The energy of an electron in an H - atom is given by $$E_n=(-2.18 \times10^{-18})/n^2~\mathrm J.$$ The shortest wavelength of light that can be used to remove an electron completely from $$n = 2$$ orbit will be:

 1 $$3647~\mathring{\mathrm A}$$ 2 $$5132~\mathring{\mathrm A}$$ 3 $$3017~\mathring{\mathrm A}$$ 4 None of these



Subtopic:  Hydrogen Spectra |
61%
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The wavelength of an electron moving with a velocity of 2.05 × 107 m s-1  would be:

$$1 .$$ $$4 . 65$$ $$\times$$ $$\left(10\right)^{- 12}$$ $$m$$

$$2 .$$ $$3 . 55$$ $$\times$$ $$\left(10\right)^{-11}$$ $$m$$

$$3 .$$ $$2 . 34$$ $$\times$$ $$\left(10\right)^{11}$$ $$m$$

$$4 .$$ $$6 . 43$$ $$\times$$ $$\left(10\right)^{ -11}$$ $$m$$

Subtopic:  De Broglie Equation |
77%
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The kinetic energy of an electron is $$3.0 \times 10^{-25}~ \mathrm J.$$ Its wave length would be:

 1 $$8.96 \times 10^{-7}~ \mathrm m$$ 2 $$4.37 \times 10^{-6}~ \mathrm m$$ 3 $$1.32 \times 10^{-7}~ \mathrm m$$ 4 $$2.89 \times 10^{-4}~ \mathrm m$$
Subtopic:  De Broglie Equation |
55%
From NCERT
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The lowest value of n for 'g' orbitals is :
1. 4
2. 5
3. 3
4. 1

Subtopic:  Shell & Subshell |
71%
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