1. The electronic configuration of an element is 1s^{2}, 2s^{2}, 2p^{6}, 3s^{2}, 3p^{6}, 3d^{5}, 4s^{1}. This represents its:

a) excited state

b) ground state

c) cationic form

d) anionic form

Discussion

Explanation: The given electronic configuration is ground state for chromium.

2. Select the pairs of ions which have same electronic configuration?

a) Cr^{3+}, Fe^{3+}

b) Fe^{3+}, Mn^{2+}

c) Fe^{3+}, Co^{3+}

d) Se^{3+}, Cr^{3+}

Discussion

Explanation: Fe

^{3+}and Mn

^{2+}have same electronic configuration

3. Many elements have non-integral atomic masses because:

a) they have isotopes

b) their isotopes have non-integral masses

c) their isotopes have different masses

d) Both a and c

Discussion

Explanation: Non-integral atomic masses are due to isotopes which have different masses.

4. Light of wavelength l shines on a metal surface with intensity x and the metal emits electrons per second of average energy, Z. What will happen to Y and Z if x is doubled?

a) Y will be double and Z will become half

b) Y will remain same and Z will be doubled

c) Both Y and Z will be doubled

d) Y will be doubled but Z will remain same

Discussion

Explanation: When intensity is doubled, number of electrons emitted per second is also doubled but average energy of photoelectrons emitted remains the same.

5. Difference between n^{th} and (n + 1)^{th} Bohr's radius of H-atom is equal to its (n – 1)^{th} Bohr's radius. The value of n is:

a) 1

b) 2

c) 3

d) 4

Discussion

Explanation: r

_{n}∞ n

^{2}

But r

_{n}+ 1 – r

_{n}= r

_{n}– 1

(n + 1)

^{2}– n

^{2}= (n – 1)

^{2}

n = 4

6. Atoms consists of protons, neutrons and electrons. If the mass of neutrons and electrons were made half and two times respectively to their actual masses, then the atomic mass of \[_{6}{{C}^{12}}\]

a) Will remain approximately the same

b) Will become approximately two times

c) Will remain approximately half

d) Will be reduced by 25%

Discussion

Explanation: No change by doubling mass of electrons however by reducing mass of neutron to half total atomic mass becomes \[6+3\] instead of \[6+6\] . Thus, reduced by 25%.

7. Principal, azimuthal and magnetic quantum numbers are respectively related to:

a) size, orientation and shape

b) size, shape and orientation

c) shape, size and orientation

d) none of these

Discussion

Explanation: Principal gives size, azimuthal gives shape and magnetic quantum number gives the orientation.

8. The number of d-electrons retained in Fe^{2+} (At.no. of Fe = 26) ion is

a) 4

b) 5

c) 6

d) 3

Discussion

Explanation: Configuration of Fe

^{+2}= 3d

^{6}.4s°

9. Consider the ground state of Cr atom (Z=24). The number of electrons with the azimuthal quantum numbers 1 = 1 and 2 are respectively

a) 12 and 4

b) 16 and 5

c) 16 and 4

d) 12 and 5

Discussion

Explanation: Configuration of Cr (Z = 24) is 1s

^{2}2s

^{2}2p

^{6}3s

^{2}3p

^{6}3d

^{5}4s*

1 = 1, denotes p-electrons (2p

^{6}, 3p

^{6})

1 = 2, denotes d-electrons (3d

^{5})

10. The electrons identified by quantum numbers n and l

1) n = 4, l = 1 2) n = 4, l = 0

3) n = 3, l = 2 4) n = 3, l = 1

can be placed in order of increasing energy as

a) c < d < b < a

b) d < b < c < a

c) b < d < a < c

d) a < c < b < d

Discussion

Explanation: Greater the (n + l) value, greater is the energy. If (n + l) values are equal, then greater the ‘n’ value greater is the energy.