NIOS Class 12 Physics Chapter 26 Nuclei and Radioactivity

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NIOS Class 12 Physics Chapter 26 Nuclei and Radioactivity

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Nuclei and Radioactivity

Chapter: 26

Module – VII: Atoms And Nuclei

INTEXT QUESTIONS 26.1

1. Make groups of Isotopes, Isobars and Isotones from the following collection of different atoms:

Ans: Isotopes are atoms with same atomic number Z, but  different mass number A):

(i) Carbon isotopes: 12/6 C and 14/6 C

(ii) Hydrogen isotopes: 1/1 H, 2/1 H, and 3/1 H

(iii) Oxygen isotopes: 16/8 O and 18/8 O

(iv) Lead isotopes: 206/82 Pb and 207/82 Pb

(v) Chlorine isotopes: 35/17 Cl and 37/17 Cl

(vi) Uranium isotopes: 235/92 U and 239/92 U

Isobars (Same mass number A, different atomic number Z):

(i) Mass number 76: 76/32 Ge and 76/34 Se

(ii) Mass number 40: 40/18 A and 40/20 Ca

(iii) Mass number 7: 7/3 Li and 7/4 Be

(iv) Mass number 3: 3/1 H and 3/2 He

(v) Mass number 27: 27/13 Al and 27/12 Mg

Isotones (Same number of neutrons N = A – Z):

(i) N = 1 (1 neutron): 2/1 H and 3/2 He

(ii) N = 8 (8 neutrons): 14/6 C and 16/8 O

(iii) N = 10 (10 neutrons): 18/8 O and 20/10 Ne (if present)

(iv) N = 12 (12 neutrons): 23/11 Na and 24/12 Mg (if 24/12 Mg were present)

(v) N = 14 (14 neutrons): 27/13 Al and 28/14 Si

(vi) N = 20 (20 neutrons): 40/18 A and 40/20 Ca

2. Fill in the blanks:

(i) Neutron is __________ than proton.

Ans: Heavier.

(ii) The total number of protons and neutrons in an atom is called the _________ number of that atom.

Ans: Mass.

(iii) The protons and neutrons together are called ___________.

Ans: Nucleons.

(iv) The number of neutrons in 27/13 Al = _________.

Ans: 14 (N = A – Z = 27 – 13 = 14).

(v) The number of protons in 28/14 Si = ________.

Ans: 14 (Z = 14)

(vi) Two atoms are said to belong to different elements if their ____________ numbers are different.

Ans: Atomic.

3. Which number cannot be different in two atoms of the same element – mass number, atomic number, neutron number?

Ans: The atomic number cannot be different in two atoms of the same element. The atomic number (Z) represents the number of protons in the nucleus, which defines the identity of an element. All atoms of the same element must have the same number of protons, hence the same atomic number. However, atoms of the same element can have different mass numbers (A) due to different numbers of neutrons, making them isotopes. They can also have different neutron numbers (N = A – Z) while maintaining the same atomic number. For example, carbon-12 and carbon-14 are both carbon atoms with Z = 6, but they have different mass numbers (12 and 14) and different neutron numbers (6 and 8 respectively).