Decide which element probably forms a compound with hydrogen that has a chemical formula most and least similar to the chemical formula of the compound formed by hydrogen and sulfur.

Most similar- oxygen

Least similar- sodium

Explanation:

The complete question is shown in the image attached.

Now let us consider all the options in the questions carefully. We do know that hydrogen forms  covalent bonds with sulphur. Two hydrogen atoms form form two polar covalent bonds with one sulphur atom. The molecule is bent owing to the presence of two lone pairs of electrons on the sulphur central atom.

Oxygen is in the same group as sulphur in the periodic table. The compound between hydrogen and sulphur is strikingly similar to the compound formed between sulphur and hydrogen due to chemical similarity of compounds of elements in the same group of the periodic table. Hence H2O bears the greatest similarity to H2S.

The bond between hydrogen and halogens is also polar covalent but less similar to the bond between sulphur and hydrogen.

Lastly, the bond between hydrogen and sodium is ionic and least similar to the bond between hydrogen and sulpur. We actually have in that compound, Na^+ H^-. Sodium transfers one electron to hydrogen as is implied in the ionic formula shown.

Hence the answer above.