Question

From the symbol ${}_2{}^4\mathrm{He}$ for the element helium, write down the mass number and the atomic number of the element.

Answer 1

• Atomic number(Z)- The total number of protons in the nucleus of an atom gives us the atomic number of that atom.
• Mass number(A)- The number of protons and neutrons combine to give us the mass number of an atom.
• The atoms are written in this manner ${}_{\mathrm{Z}}{}^{\mathrm{A}}\mathrm{X}$ where A denotes mass number and Z denotes the atomic number.

Hence, the symbol ${}_2{}^4\mathrm{He}$ tells us that-

• 4 is the mass number(A) of the element Helium.
• 2 is the atomic number(Z) of the element Helium.