# Objective questions of atoms and nuclei

This assignment contain all important objective questions of atoms and nuclei , which is important for the students preparing for board examination and other competitive examinations .

**Atomic Structure **

**According to Bohr’s atomic model:**

(a)an atom has heavy, positively charged nucleus

(b)the electron radiates energy only when it jumps to another orbit

(c)the electron can move only in particular orbits

(d)all the above statements are correct

**In an atom, two electrons move around the nucleus in circular orbit of radii R and 4R. The ratio of the time taken by them to complete one revolution is:**

(a)1/4 (b) 4/1 (c) 8/1 (d) 1/8

**According to Bohr’s quantum condition, an electron can revolve only in those orbits in which:**

(a) its energy is an integral multiple of h/2π

(b) its linear momentum is an integral multiple of h/2π

(c) its angular momentum is an integral multiple of h/2π

(d) its angular momentum vector is perpendicular to magnetic dipole moment vector

**According Bohr’s theory the radius of the electron in an orbit described by principal quantum number n and atomic number Z is proportional to:**

(a)Z^{2}n^{2 }(b) Z^{2 }/n^{2 }

(c) Z^{2 }/n

(d) n^{2}/Z

**When the electron jumps from a level n = 4 to n = 1, the momentum of the recoiled hydrogen atom will be:**

(a)5 ₓ 10^{-27}kg – ms^{-1 }

(b) 13.6 ₓ 10^{-19}kg – ms^{-1 }(c)75 ₓ 10^{-19}kg – ms^{-1 }

(d) zero

**The radius of Bohr’s fast orbit is a**_{0}. The electron in nth orbit has a radius:

(a)na_{0}

(b) a_{0}/n

(c) n^{2}a_{0}

(d) a_{0}/n^{2}

**The angular momentum of an electron in the nth orbit is given by:**

(a)nh

(b) h/2πn

(c) nh/2π

(d) n^{2}h/2π

**When a hydrogen atom is raised from the ground state to fifth state:**

(a)both KE and PE increase

(b) PE increases and KE decreases

(c)both KE and PE decrease

(d) PE decreases and KE increases**As the electron in Bohr orbit of hydrogen atom passes from state n = 2 to n = 1, the KE (K) and PE (U) change as: (a)K two-fold, U also two-fold**

(c) K four-fold, U two-fold

(b)K four-fold, U also four-fold

(d) K two-fold U four-fold**An electron jumps from the 4**^{th}orbit to the 2^{nd}orbit of a hydrogen atom. Given the Rydberg constant R = 10^{5}cm^{-1}, the frequency in Hz of the emitted radiation will be:

(a)3/16 ₓ 10^{5}

(b) 3/16 ₓ 10^{15}

(c) 9/16 ₓ 10^{15}

(d) 3/4 ₓ 10^{15}**Nitrogen gas, cynogen gas and compounds of carbon give band spectra because:**

(a)these are excited in molecular state

(b)these are in atomic state

(c)these are inorganic compounds

(d)these are in gaseous state**The hydrogen atom can give spectral lines in the series, Lyman, Balmer and Paschen. Which of the following statements is correct?**

(a)Lyman series is in the infrared region

(b)Balmer series is in the visible region (partly)

(c)Balmer series is solely in the ultraviolet region

(d)Paschen series is in the visible region**.Which of the following statements is true regarding Bohr’s model of hydrogen atom?**

(a)Orbiting speed of electron decreases as it falls to discrete orbits away from the nucleus.

(b)Radii of allowed orbits of electrons are proportional to the principal quantum number.

(c)Frequency with which electrons orbits around the nucleus in discrete orbits is inversely proportional the principal quantum number.**Binding force with which the electron is bound to the nucleus increases as it shifts to outer orbits.**

(A)a and c

(B) b and d

(C) a, b and c

(D) b, c and d**An electron in the hydrogen atom jumps from excited state n to the ground state. The wavelength so emitted illuminates a photosensitive material having work function 2.75 eV. If the stopping potential of the photo-electron is 10 V, then the value of n is:**(a)2 (b) 3 (c) 4 (d) 5

**In Bohr’s model, the atomic radius of the fast orbit is r**(a)r_{0};then the radius of the third orbit is:

_{0}/9 (b) r_{0 }(c) 9r_{0 }(d) 3r_{0}**The ground state energy of H-atom is 13.6 eV. The energy needed to ionise H-atom from its second excited state is:**(a)51 eV (b) 3.4 eV (c) 13.6 eV (d) 12.1 eV**Hydrogen atoms are excited from ground state to the state of principal quantum number 4. Then, the number of spectral lines observed will be:**

(a) 3 (b) 6 (c) 5 (d) 2**If an electron in n = 3 orbit of hydrogen atom jumps down to n = 2 orbits, the amount of energy released and the wavelength of radiation emitted are:**(a)85 eV, 6566 Å (b) 1.89eV, 1240 Å (c) 1.89 eV, 6566 Å (d) 1.5 eV,6566 Å

**The longest wavelength that a single ionised helium atom in its ground state will absorb is:**

(a)912 Å (b) 304 Å (c) 606 Å (d) 1216 Å-
**If the ionisation potential of hydrogen atom is 13.6 eV, the energy required to remove the electron from the third orbit of hydrogen atom is:**

(a)5 V (b) 1.5 eV (c) 4.5 eV (d) 3.4 V **The ratio of the areas within the electron orbits for the first excited state the ground state for the ground state for the hydrogen atom is:**(a)2 : 1 (b) 4 : 1 (c) 8 : 1 (d) 16 : 1**The first excitation potential of the hydrogen atom in the ground state is:**(a)6 volt (b) 10.2 volt (c) 3.4 volt (d) 1.89 volt

**The minimum energy in electron volt required to strip a ten times ionized sodium atom ( i.e., Z = 11) of its last electron is:**

(a)6 eV (b) 13.6/11 eV (c) 13.6 ₓ 11 eV (d) 13.6 ₓ (11)^{2}eV-
**Of the following transitions in hydrogen atom, the one which gives emission line of minimum frequency is:**(a)n = 1 to n = 2 (b) n = 3 to n = 10 (c) n = 10 to n = 3 (d) n = 2 to n = 1 **The energy of an electron in the nth orbit of positronium is:**(a) -13.6/n

^{2}eV (b) -13.6 ₓ 2/n^{2}eV (c) -13.6 ₓ 4/n^{2}eV (d) -13.6/2n^{2 }eV**The ratio (in SI units) of magnetic dipole moment to that of the angular momentum of electron of mass m kg and charge e coulomb in Bohr’s orbit of hydrogen atom is:**

(a) e/2m (b) e/m (c) 2e/m (d) none of these-
**The Bohr model of atoms:**

(a)assumes that the angular momentum of the electrons is quantized

(b)uses Einstein’s photoelectric equation

(c)predicts continuous emission spectra for atoms

(d)predicts the same emission spectra for all types of atoms -
**The angular momentum of an electron in a hydrogen atom is proportional to:**

(a)1/√r (b) 1/r (c) √r (d) r^{2} -
**What will be the angular momentum in fourth orbit, if L is the angular momentum of the electron in the second orbit of hydrogen atom?**

(a)2 L (b) 3/2 L (c) 2/3 L (d) L/2 -
**The required energy to detach one electron from Balmer series of hydrogen spectrum is:**

(a)6 eV (b) 10.2 eV (c) 3.4 eV (d) -1.5 eV -
**Which of the following is quantised according to Bohr’s theory of hydrogen atom?**(a)Linear momentum of electron

(b)Angular momentum of electron

(c)Angular velocity of electron

(d)Linear velocity of electron **The energy levels of a certain atom for 1**^{st},2^{nd}and 3^{rd}levels are E, 4E/3 and 2E respectively. A photon of wavelength λ is emitted for a transition 3 →1.What will be the wavelength of emission for transition 2 → 1?

(a) λ/3 (b) 4λ/3 (c) 3λ/4 (d) 3λ**The ratio of the frequencies of the long wavelength limits of the Lyman and Balmer series of hydrogen is:**

(a)27 : 5 (b) 5 : 27 (c) 4 : 1 (d) 1 : 4**If electron in a hydrogen atom has moved from n = 1 to n = 10 orbit, the potential energy of the system has:**

(a)Increased (b)Decreased (c) remains unchanged (d) become zero**The energy of hydrogen atom in nth orbit is E**_{n}, then the energy in nth orbit of singly ionised helium atom will be:

(a)4E_{n}(b) E_{n}/4 (c) 2E_{n}(d) E_{n}/2**The energy of hydrogen atom is -13.6 eV in the first orbit, then calculate the energy of He atom in the same orbit:**

(a)6 eV (b) -27.2 eV (c) -54.4 eV (d) +54.4 eV-
**In hydrogen spectrum, the shortest wavelength in Balmer series is λ. The shortest wavelength in Brackett series will be:**(a)2λ (b) 4λ (c) 9λ (d) 16λ **The ratio of the largest to shortest wavelength in Lyman series of hydrogen spectra is:**

(a) 25/9 (b) 17/6 (c) 9/5 (d) 4/3**The minimum orbital angular momentum of the electron in hydrogen atom is:**

(a) h (b) h/π (c) h/2π (d) h/2**The total energy of an electron in the first excited state of hydrogen atom is about – 3.4 eV. Its KE in this state is:**

(a)4 eV (b) 6.8 eV (c) -3.4 eV (d)-6.8 eV**The ground state energy of hydrogen atom is -13.6 eV. What is the potential energy of the electron in this state?**

(a)0 eV (b) -27.2 eV (c) 1 eV (d) 2 eV**If λ**_{1}and λ_{2}are the wavelengths of the first member of the Lyman and Paschen series respectively, then λ_{1}: λ_{2}is:

(a)1 : 3 (b) 1 : 30 (c) 7 : 50 (d) 7 : 108

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