Question

Which of the following are true for an element?

(i) Atomic number = number of protons + number of electrons

(ii) Mass number = number of protons + number of neutrons

(iii) Atomic mass = number of protons = number of neutrons

(iv) Atomic number = number of protons = number of electrons\

A.
(i) and (ii)

B.
(i) and (iii)

C.
(ii) and (iii)

D.
(ii) and (iv)

Answer 1

C. (ii) and (iii) is correct

Explanation:

The correct formulas are :-

- Atomic number = Number of protons present in the nucleus is called atomic number (Z) of an element. there is no formula. it just a number of protons only.

Note:- The atomic number symbol, Z, stands for “Zahl,” meaning German number.

Hence, option (i) and (iv) are wrong

- mass number = protons + neutrons

i.e, subtract the number of protons, or atomic number, from the mass number.

- A = Z + n° Example: 19K39. Z = 19 and A = 39

where ,

A = atomic mass number

z = number of protons = atomic number

n° = number of neutron

in simple word, sum of mass number of proton and mass number of neutron is called atomic weight or atomic mass