If the protons and electrons are the only basic charges in the universe, all the observable charges have to be integral multiples of e. Thus, if an object contains x electrons and y protons, the net charge on the object will be
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( (y - x)e \)
Charge is quantised, so the net charge is the algebraic sum of the charges of the particles. A proton carries \( +e \) and an electron carries \( -e \).
\( \displaystyle q = y(+e) + x(-e) = (y - x)e \)
Protons and electrons carry opposite signs, so they cannot be added as \( (x + y)e \); the electrons are subtracted from the protons.
Note: This question is from NCERT (2026-27). NTA sets numerical questions from NCERT too, so do not ignore NCERT while practising numericals.
NCERT (2026-27):
Quantisation of Charge – “… If the protons and electrons are the only basic charges in the universe, all the observable charges have to be integral multiples of e. Thus, if a body contains n1 electrons and n2 protons, the total amount of charge on the body is n2 × e + n1 × (–e) = (n2 – n1) e.”