Mendeleev’s principle of chemical periodicity states that when the elements are arranged according to their atomic numbers. this periodic law allows elements with similar properties to appear at regular intervals. predict the group of elements and their number of valence electrons that will combine in a 2: 1 ratio to with sodium. a) bromine, chlorine, iodine, 7 b) sulfur, selenium, polonium, 6 c) hydrogen, fluorine, potassium, 1 d) calcium, phosphorus, tellurium, 2

The highlight of this question is the "2:1 ratio."
On the periodic table, bromine, chlorine, and iodine have 7 valence electrons while sulfur, selenium, and polonium have 6, and so these options are feasible founded on their valence electrons. Though, fluorine does not have 1 valence electron and phosphorus and tellurium do not have 2 valence electrons, so C) and D) are spontaneously out, leaving A) and B).
If we know that the sodium will mix in a 2:1 ratio, we know that the charge of the ions must have a 2:1 ratio too; that's how ionic compounds effort. Sodium (Na) has an ion with a charge of +1 (Na+), so in other words, at all ion it mixes with in a 2:1 ratio must have a charge of -2.
Therefore, sulfur, selenium, and polonium have charges of -2.