UPSC CAPF AC 2019 Paper

The atomic number, Z, of any element, is the number of protons, positively charged nuclear particles, contained in the nucleus. The atomic number of Uranium is 92. In case of Uranium-235, the mass number (235) is the sum of the number of protons, and the number of neutrons.
So, Mass number of Uranium–235 = 235 = 92 + Number of neutrons
So, the number of neutrons = 235 – 92 = 143