4 Which pair of ions is isoelectronic? A Ca2+ and 02-
B Na+ and 02-
OC Lit and Cl-
OD Mg2+ and CI-

B. Na+ and O2-

Explanation:

Na+ plus has 10 electrons and O2- also has 10 electrons

When magnesium is burned, it reacts with oxygen in air not with the fire. The fire is the energy needed for the reaction to happen. Magnesium reacts with oxygen forming magnesium oxide. The light emitted from the reaction is because the reaction produced a lot of heat.