Question

A nucleus represented by the symbol ${}_{Z}^{A}X$ has:
A. Z protons and A-Z neutrons
B. Z protons and A neutrons
C. A protons and Z+A neutrons
D. Z neutrons and Z-A protons.

Answer 1

Hint: In ${}_{Z}^{A}X$ , X represents the chemical element, A represents the mass number or molecular weight of the element, Z represents the atomic number of the chemical element. All the elements in the periodic table have atomic number and mass number.

Complete step by step solution:
- In the given question there is the symbol ${}_{Z}^{A}X$ .
- We have to say what A represents and What Z is going to represent from the given symbol.
- We know that the number of protons in the nucleus of the atom is equal to the atomic number (Z) of the nucleus.
 - Means Z represents the number of protons in the nucleus.
- Mass number = number of protons + number of neutrons.
- The number of neutrons in the nucleus is equal to the difference between the mass number (A) of the nucleus and atomic number (Z) of the nucleus.
Number of neutrons = A – Z
- Means A-Z represents the number of neutrons in the nucleus of the atom.

So, the correct option is A.

Note: Take an example of ${}_{6}^{12}C$. In carbon the atomic number (Z) = 6 means the number of protons present in the carbon atom are 6.
The mass number of the carbon is (A) = 12.
The number of neutrons in the carbon nucleus is = A – Z = 12 – 6 = 6.