Which of these pairs of elements have the same number of valence electrons?

...... The answer is : c) carbon (C) and lead (Pb)

Both carbon and lead belong to Group IV elements, and thus they have the same number of valence electrons.

In each of the other options, the two elements belong to different groups, and thus they do NOT have the same number of valence electrons.

All of the elements in a family (a vertical column in the periodic table) have the same number of valence electrons. You can determine the number of valence electrons from the Roman numeral at the top of each column.

Number of valence electrons in each atom
a) oxygen (O) and bromine (Br) ........ O=6, Br=7
b) selenium (Se) and bromine (Br) .... Se=6, Br=7
c) carbon (C) and lead (Pb) ............... C=4, Pb=4
d) oxygen (O) and carbon (C) ............ O=6, C=4
e) sodium (Na) and magnesium (Mg).. Na=1, Mg=2