Which two chemical species represent a pair of isotopes and why?

CBSE Class 9 CBSE Class 9 Science
1

Number of electrons, protons and neutrons in chemicals species A, B, C and D is given below:

Chemical Species Electrons Protons Neutrons
A 2 3 4
B 10 9 8
C 8 8 8
D 8 8 10

Answer the following questions:

  1. What is the mass number of A and B?
  2. What is the atomic number of B?
  3. Which two chemical species represent a pair of isotopes and why?
  4. What is the valency of element C? Also, justify your answer.
2
  1. Mass number of A = 3 + 4 = 7
    Mass number of 6 = 9+8 = 17
  2. Atomic number of 6 = Number of protons = 9
  3. C and D are isotopes as they have same atomic numbers but different mass numbers
  4. Electronic configuration of image
    It needs two electrons to complete its octet. Hence, its valency is 2.