Sulfur powder (S) and oxygen gas (O2) undergo a chemical reaction to form sulfur dioxide (SO2).
Which equation represents this chemical reaction?

S (s) + O₂ (g) → SO₂ (aq) represents this chemical reaction

In stating a chemical equation it can be done in the form of a word or a chemical formula

A word equation will include the words of the reactants, products, form of the compound (liquid, gas, solid), the total concentration/quantity of the reactants and products which can be expressed in mass, moles, or volume

The questions statement above shows that sulfur powder (S) and oxygen gas (O₂) are reactants (located on the left of the reaction equation), and sulfur dioxide (SO₂) is the product of the reaction (stated in the problem there is the word "to form") which is located on the right

So the complete reaction

S (s) + O₂ (g) → SO₂ (aq)