Answer: Option (C) is the correct answer.
Explanation:
Bromine is a group 7A element with atomic number 35. Whereas magnesium is a group 2A element with atomic number 12.
This means that a neutral atom of bromine has more number of electrons as compared to a neutral atom of magnesium. Hence, size of a bromine atom will definitely be larger than the size of a magnesium atom.
Thus, we can conclude that we know that a neutral atom of bromine (Br) is larger than a neutral atom of magnesium (Mg) because atoms with many electrons are always larger than atoms with fewer electrons, a neutral atom of bromine has 35 electrons while neutral atom of magnesium has only 12.