Question

Consider the following table:

Element	Atomic no.	No. of neutrons
A	3	4
B	9	10
C	13	14
D	17	18
E	18	22

(i) How many protons are there in an atom of D?
(ii) What is the mass number of B?
(iii) Write electron distribution of C.
(iv) What is the valency of E?
(v) What is the number of electrons present in a monovalent positive cation of A and a monovalent anion of D?

Answer 1

(i) Number of protons in D:

1. The atomic number of element D is 17.
2. Thus, the number of protons is 17.

(ii) Mass number of B:

1. The atomic number of element B is 9 and the number of neutrons is 10.
2. Thus, the number of both electrons and protons in element B is 9.
3. Hence, the mass number (total number of protons and neutrons) of B is 17 (9+10).

(iii) Electron distribution of C:

1. The atomic number of C is 13.
2. Thus, the number of electrons in element C is 13.
3. The electron distribution of C is 2, 8, 3.

(iv) Valency of E:

1. The atomic number of E is 18.
2. So, the electron distribution of E is 2, 8, 8.
3. The outermost shell is completely filled and thus the valency is zero.

(v) Number of electrons in a monovalent positive cation of A and a monovalent anion of D:

1. The atomic number or the number of electrons in A is 3.
2. If one electron is removed, A becomes a monovalent cation with 2 electrons.
3. The atomic number or the number of electrons in D is 17.
4. If one electron is added, D becomes a monovalent anion with 18 electrons.