Which elements combine by forming an ionic bond
a) sodium and potassium
b) sodium and oxygen
c) carbon and oxygen
d) carbon and sulfur

B) Sodium and oxygen

Explanation:

Ionic bond: This type of bond is formed when there is a complete transfer of electrons from one element to another element. Ionic bond is the bond which is formed between the two oppositely charged ions and are held by the strong electrostatic attraction. This is formed between the atoms which have high differing electronegativities. In this bonding one element is always a metal and another is a non-metal.

Thus,

Out of the options, B involves a metal and a nonmetal which is sodium and oxygen respectively. Thus, they can form a ionic bond on combining.

A) represents 2 metals, C) and D) represents 2 nonmetals and thus, they cannot form an ionic bond.

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6