Question

Find the relative atomic mass of an element made up of six protons and seven neutrons.

• A. 12.98 u
• B. 13 u
• C. 12.38 u
• D. 13.98 u

Answer 1

The correct option is A 12.98 u

Relative atomic mass is the mass of an atom of an element compared to one-twelth the mass of C-12 atom.
Given element is made up of 6 protons and 7 neutrons.
Atomic mass = Mass of protons + Mass of neutrons
Mass of one proton = 1 u = Mass of one neutron
Atomic mass of given element = (6 + 7) u = 13 u
Atomic mass of C-12 isotope is : 12.01 u
Relative atomic mass = $\frac{massof1atomoftheelement}{\frac{1}{12}\times massof1atomofcarbon-12isotope}$

= $\frac{13}{\frac{1}{12}\times 12.01}$
=12.98 u.