# Class 11 Chemistry MCQ – Bohr’s Model for Hydrogen Atom

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This set of Class 11 Chemistry Chapter 2 Multiple Choice Questions & Answers (MCQs) focuses on “Bohr’s Model for Hydrogen Atom”.

1. Angular momentum of an electron is quantized.
a) True
b) False

Explanation: According to Bohr’s postulate, angular momentum is quantized and this is given by the expression mevr = nh/2π. (n =1, 2, 3….). mevr is the angular momentum and h is the Planck’s constant. Movement of an electron can only be possible in orbits whose angular momentum is the integral multiple of h/2π

2. The energy of 1st orbit in a hydrogen atom __________
a) 3.18×10–12 J
b) –2.18×10–18 J
c) –3.18×10–18 J
d) 2.18×10–18 J

Explanation: The energy of an nth orbit in a hydrogen atom is given by the formula En = -RH/n2, where is the energy of nth orbit and RH is the Rydberg constant. The energy of 1st orbit in a hydrogen atom = -2.18 x 10-18 J/1 = -2.18 x 10-18 J.

3. What is the ratio of the atomic radius of the 5th orbit in chlorine atom and 3rd orbit in Helium atom?
a) 153:50
b) 50:153
c) 153:100
d) 100:153

Explanation: The atomic radius of an atom is given by the formula rn = 52.9n2/Z pm, where rn is the radius of nth orbit of an atom and Z is the atomic number of that atom. The ratio of the atomic radius of the 5th orbit in chlorine atom and 3rd orbit in Helium atom is 25/17:9/2 = 50:153.
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4. What’s the radius of 1st orbit of He+ atom?
a) 0.1058 nm
b) 0.2156 nm
c) 0.00529 nm
d) 0.02645 nm

Explanation: The atomic radius of an atom is given by the formula rn = 52.9n2/Z pm, where rn is the radius of nth orbit of an atom and Z is the atomic number of that atom. For He+, n = 1 and Z =2. Radius = 52.9(1)/2 pm = 0.02645 nm.

5. Bohr’s model couldn’t explain Zeeman and stark effect.
a) False
b) True

Explanation: Yes, it’s a limitation of Bohr’s model that it could not the splitting of spectral lines in the magnetic field that is Zeeman effect and also in the electric field also known as a stark effect. so the above statement is true.
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6. Bohr’s model could not explain the ability of atoms to form molecules by ______
a) Attraction
b) Physical bonds
c) Chemical bonds
d) Polarity

Explanation: Though Bohr’s postulates could explain angular momentum, radius, and energy of an orbit, line spectrum of the hydrogen atom, it also had some drawbacks. Among the drawbacks not able to explain the ability of atoms to form molecules by chemical bonds is also one.

7. Calculate the wavelength of a photon that traveled from 5th orbit to 2nd orbit.
a) 434 nm
b) 456 nm
c) 863 nm
d) 268 nm

Explanation: The energy of an nth orbit in a hydrogen atom is given by the formula En = -RH/n2, where is the energy of nth orbit and RH is the Rydberg constant. E5 – E2 = -4.58 x 10-19J. λ(wavelength) = c(speed of light)h(Planck’s constant)/E = 434nm.

8. The energy of a hydrogen atom is positive.
a) True
b) False

Explanation: The energy of a hydrogen atom is negative. It means the energy of a hydrogen atom is then that lower than that of a free electron that is at rest. This means the hydrogen atom has negative electronic energy.

9. Which of the following is the value for Rydberg constant?
a) 2.95 x 10-18 J
b) -2.95 x 10-18 J
c) -2.18 x 10-18 J
d) 2.18 x 10-18 J

Explanation: The energy of an nth orbit in a hydrogen atom is given by the formula En = -RH/n2, where is the energy of nth orbit and RH is the Rydberg constant. When experiments were conducted, the product of the energy of nth orbit to the square of n is constant i.e. Rydberg constant.

10. Iω = _________
a) mev2r
b) mevr2
c) mer
d) mevr

Explanation: We know that linear momentum is given by mv and that angular momentun in Iω; m = mass, v = velocity, r = radius, I = inertia of momentum and w = angular velocity. I =mer2 and ω = v/r and Iω = mer2v/r = mevr.

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