# Atomic Number and Isotopes - MCQs with answers

## Atomic Number and Isotopes - MCQs with answers

Q1. Particles having the same atomic number but different mass number are called_____.

a. β particle
b. neutrons
c. Isotope
d. Isomer

Explanation: Isotopes are defined as the elements having same atomic number but they differ in their mass number and chemical characteristics.

Eg: Carbon - diamond and graphite. Uranium - 92U234, 92U235, 92U238

Q2. Which isotope of uranium is used for the nuclear fission reaction

a. U-234
b. U-235
c. U-238
d. U-233

Explanation: the U-235 isotope of uranium is easily and readily fissionable. When a neutron enters a U-235 atom there is a possibility that the nucleus will split and release the enormous amount of energy that binds the nucleus together. The uranium nucleus ejects two or three neutrons resulting in chain reaction.

Q3. One atomic mass unit is equivalent to________.

a. 931.4 MeV
b. 251.2 MeV
c. 120.4 MeV
d. 892.4 MeV

Explanation: from Einsteinâ€™s law, W = mc2

1 amu = 1.66 * 10-27 *(3*108)2

= 1.494 * 10-10 J

1 eV = 1.602 * 10-19 J

Also, 1 J = 1/ (1.602 * 10-13) MeV

1 J = 1/ (1.494 * 10-10) amu

1 amu = (1.494 * 10-10) / (1.602 * 10-13)

= 931 MeV