MCQs on Aufbau Principle

The aufbau principle is used to fill electrons in different orbitals. The aufbau principle is based on relative energies of orbitals. It takes into account Pauli’s exclusion principle and the Hund’s rule. According to this principle, electrons are filled in the orbitals in order of their increasing energies. The orbital with lower energy is filled first before filling the higher energy orbitals.

1. All four quantum numbers cannot be the same for any two electrons in an atom. This principle is known as

(a) Aufbau principle

(b) Hund’s Rule

(c) Pauli’s Exclusion principle

(d) None of the above

2. What is the correct order of orbitals in which electrons are filled?

(a) 4s, 3d, 4p, 5s, 4d

(b) 3d, 4s, 4p, 4d, 5s

(c) 3d, 4p, 4s, 4d, 5s

(d) 5s, 4p, 3d, 4d, 5s

3. What is the correct electronic configuration of an atom (Cu) with atomic number 29?

(a) 1s2, 2s22p6, 3s23p63d10, 4s1

(b) 1s2, 2s22p6, 3s23p6, 4s2 3d9

(c) 1s2, 2s22p6, 3s23p6, 4s24p63d3

(d) 1s2, 2s22p6, 3s23p6, 4s24p6, 5s25p1

4. Which of the following ions has 18 electrons in the outermost shell?

(a) Th4+

(b) Cu+

(c) K+

(d) Cs+

5. According to the aufbau principle

(a) electrons enter the lowest available energy level

(b) only two electrons can occupy an orbital

(c) orbitals are regions where one is likely to find an electron

(d) electrons tend to remain unpaired

6. Three unpaired electrons are present in

(a) O

(b) N

(c) C

(d) B

7. The electrons will enter which of these orbitals after filling the 3d orbitals completely?

(a) 4d

(b) 4f

(c) 4s

(d) 4p

8. Which of the following is incorrect about ‘s’ orbitals?

(a) They are spherical in shape

(b) They can only hold one electron

(c) They are found in all principal energy levels

(d) None of these

9. What is the correct electronic configuration of an atom with atomic number 8?

(a) 1s2 2s2 2p6

(b) 1s2 2s6

(c) 1s2 2s2 2p4

(d) 2s2 2p6

10. How many unpaired electrons are present in N2+?

(a) 0

(b) 2

(c) 3

(d) 1

Answer

1. (c)

2. (a)

3. (a)

4. (b)

5. (a)

6. (b)

7. (d)

8. (b)

9. (c)

10. (d)

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