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Atoms NEET Questions — Free MCQ Practice

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An ionic atom equivalent to hydrogen atom has wavelength equal to 1/4 of the wavelengths of hydrogen lines. The ion will be

A.

${He}^{+}$

B.

${Li}^{+ +}$

C.

${Ne}^{9 +}$

D.

${Na}^{10 +}$

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Explanation

(a) $\bar{ν} \propto \frac{1}{λ} \propto Z^{2} \Rightarrow {λZ}^{2} = constant \Rightarrow λ = \frac{λ}{4} Z^{2} \Rightarrow Z = 2$

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The third line of Balmer series of an ion equivalent to hydrogen atom has wavelength of 108.5 nm. The ground state energy of an electron of this ion will be

A.

3.4 eV

B.

13.6 eV

C.

54.4 eV

D.

122.4 eV

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Explanation

(c) For third line of Balmer series $n_{1} = 2, n_{2} = 5$

$∴ \frac{1}{λ} = {RZ}^{2} [\frac{1}{n_{1}^{2}} - \frac{1}{n_{2}^{2}}]$ gives $Z^{2} = \frac{n_{1}^{2} n_{2}^{2}}{(n_{2}^{2} - n_{1}^{2}) λR}$

On putting values Z = 2
From $E = - \frac{13.6 {(Z)}^{2}}{n^{2}} = \frac{- 13.6 (2)^{2}}{(1)^{2}} = - 54.4 eV$

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An electron in the n = 1 orbit of hydrogen atom is bound by 13.6 eV energy is required to ionize it is

A.

13.6 eV

B.

6.53 eV

C.

5.4 eV

D.

1.51 eV

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Explanation

(a) Ionization energy = Binding energy.

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Hydrogen atom emits blue light when it changes from n = 4 energy level to the n = 2 level. Which colour of light would the atom emit when it changes from the n = 5 level to the n = 2 level

A.

Red

B.

Yellow

C.

Green

D.

Violet

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Explanation

(d) In the transition from orbit $5 \to 2$ , more energy is liberated as compared to transition from $4 \to 2$

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The first line of Balmer series has wavelength 6563 Å. What will be the wavelength of the first member of Lyman series

A.

1215.4 Å

B.

2500 Å

C.

7500 Å

D.

600 Å

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Explanation

(a) $\frac{1}{λ_{Balmer}} = R [\frac{1}{1^{2}} - \frac{1}{2^{2}}] = \frac{3 R}{4} ∴ λ_{Lyman} = λ_{Balmer} \times \frac{5}{27} = 1215.4 \overset{0}{A}$

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In Bohr's model, the atomic radius of the first orbit is $r_{0}$ , then the radius of the third orbit is

A.

$\frac{r_{0}}{9}$

B.

$r_{0}$

C.

$9 r_{0}$

D.

$3 r_{0}$

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Explanation

(c) $r_{n} \propto n^{2}$

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The wavelength of the energy emitted when electron come from fourth orbit to second orbit in hydrogen is 20.397 cm. The wavelength of energy for the same transition in ${He}^{+}$ is

A.

5.099 ${cm}^{- 1}$

B.

20.497 ${cm}^{- 1}$

C.

40.994 ${cm}^{- 1}$

D.

81.988 ${cm}^{- 1}$

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Explanation

(a) $E (= \frac{hc}{λ}) \propto \frac{Z^{2}}{n^{2}} \Rightarrow λ \propto \frac{1}{Z^{2}}$

Hence $λ_{{He}^{+}} = \frac{20.397}{4} = 5.099 cm$

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Minimum excitation potential of Bohr's first orbit in hydrogen atom is

A.

13.6 V

B.

3.4 V

C.

10.2 V

D.

3.6 V

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Explanation

(c) Excitation potential = $\frac{Excitation energy}{e}$
Minimum excitation energy corresponds to excitation from n =1 to n = 2
$∴$ Minimum excitation energy in hydrogen atom = -3.4-(-13.6) = +10.2 eV

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Which of the following statements are true regarding Bohr's model of hydrogen atom

(I) Orbiting speed of electron decreases as it shifts to
discrete orbits away from the nucleus

(II) Radii of allowed orbits of electron are proportional to the cube of principal quantum number

(III) Frequency with which electrons orbits around the nucleus in discrete orbits is inversely proportional to the principal quantum number

(IV) Binding force with which the electron is bound to the nucleus increases as it shifts to outer orbits
Select correct answer using the codes given below
Codes :

A.

I and III

B.

II and IV

C.

I, II and III

D.

II, III and IV

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Explanation

(a) Orbital speed varies inversely as the radius of the orbit. Energy increases with the increase in quantum number.

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For electron moving in $n^{th}$ orbit of H-atom the angular velocity is proportional to

A.

n

B.

1/n

C.

$n^{3}$

D.

1/ $n^{3}$

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Explanation

(d) Radius of nth orbit, $r_{n} α \frac{1}{n^{2}}$

Velocity of electron, $v_{n} α \frac{1}{n}$

$∴ A n g u l a r v e l o c i t y, ω_{n} = \frac{v_{n}}{r_{n}} \Rightarrow ω_{n} α \frac{1}{n^{3}}$

Atoms MCQs for NEET — Physics Questions with Answers

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