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Atoms MCQs for NEET — Physics Questions with Answers

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Taking Rydberg’s constant $R_{H} = 1.097 \times 10^{7} m$ first and second wavelength of Balmer series in hydrogen spectrum is

2000 Å, 3000 Å

1575 Å, 2960 Å

6529 Å, 4280 Å

6552 Å, 4863 Å

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Explanation

(d) $\frac{1}{λ} = R [\frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}}]$ For first wavelength, $n_{1} = 2$ , $n_{2} = 3$ $\Rightarrow λ_{1} = 6563$ Å. For second wavelength, $n_{1} = 2, n_{2} = 4 \Rightarrow λ_{2} = 4861$ Å

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The kinetic energy of electron in the first Bohr orbit of the hydrogen atom is

– 6.5 eV

– 27.2 eV

13.6 eV

– 13.6 eV

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Explanation

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In Bohr’s model of hydrogen atom, which of the following pairs of quantities are quantized

Energy and linear momentum

Linear and angular momentum

Energy and angular momentum

None of the above

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Explanation

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The energy of the highest energy photon of Balmer series of hydrogen spectrum is close to

13.6 eV

3.4 eV

1.5 eV

0.85 eV

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Explanation

(b) $E = 13.6 [\frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}}]$ For highest energy in Balmer series $n_{1} = 2$ and $n_{2} = \infty$

$\Rightarrow E = 13.6 [\frac{1}{2^{2}} - \frac{1}{\infty^{2}}] = 3.4 eV$

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Which one of the relation is correct between time period and number of orbits while an electron is revolving in a orbit

$n^{2}$

$\frac{1}{n^{2}}$

$n^{3}$

$\frac{1}{n}$

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Explanation

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If the energy of a hydrogen atom in nth orbit is $E_{n}$ , then energy in the nth orbit of a singly ionized helium atom will be

4 $E_{n}$

$E_{n}$ /4

2 $E_{n}$

$E_{n}$ /2

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Explanation

(a) $E_{n} \propto Z^{2} \Rightarrow \frac{{(E_{n})}_{He}}{{(E_{n})}_{H}} = \frac{Z_{He}^{2}}{Z_{H}^{2}} = 4 \Rightarrow {(E_{n})}_{He} = 4 \times {(E_{n})}_{H}$

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What is the ratio of wavelength of radiations emitted when an electron in hydrogen atom jump from fourth orbit to second orbit and from third orbit to second orbit

27 : 25

20 : 27

20 : 25

25 : 27

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Explanation

(b) By using $\frac{1}{λ} = R [\frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}}]$

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As the electron in Bohr orbit of Hydrogen atom passes from state n = 2 to n = 1 , the kinetic energy K and potential energy U change as

K two-fold, U four-fold

K four-fold, U two-fold

K four-fold, U also four-fold

K two-fold, U also two-fold

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Explanation

(c)

$K E \propto \frac{1}{n^{2}} \Rightarrow \frac{K_{1}}{K_{2}} = \frac{{n_{2}}^{2}}{{n_{1}}^{2}} = \frac{4}{1} P E \propto \frac{1}{n^{2}} \Rightarrow \frac{U_{1}}{U_{2}} = \frac{{n_{2}}^{2}}{{n_{1}}^{2}} = \frac{4}{1}$

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The magnetic moment $(μ)$ of a revolving electron around the nucleus varies with principal quantum number n as

$μ \propto n$

$μ \propto 1 / n$

$μ \propto n^{2}$

$μ \propto 1 / n^{2}$

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Explanation

(a) Magnetic moment of an electron : $μ = \frac{n e h}{4 {πm}_{e}}$

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Bohr's atom model assumes

The nucleus is of infinite mass and is at rest

Electrons in a quantized orbit will not radiate energy

Mass of electron remains constant

All the above conditions

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Explanation

(d) Bohr's model assumptions-

(i) The electrons in a hydrogen atom travels around the nucleus in a circular orbit

(ii) The nucleus is of infinite mass and is at rest

(iii) Electrons in a quantized orbit will not radiate energy

(iv) Mass of electron remains constant

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