Our production and life are closely related to chemistry. Please use one or more of the five elements C, H, O, Na and Cl (reusable).

① The main components of biogas widely used in rural areas of China. The main component of biogas is methane. In methane, carbon is -4 and hydrogen is+1. Generally, the positive price comes first and the negative price comes last. This is special, so the chemical formula is CH 4；;

② It is a toxic gas, but it can be used for ironmaking. In a given element, carbon monoxide is toxic. In carbon monoxide, the valence of carbon is +2, while the valence of oxygen is -2, so the chemical formula is co.

(3) A small amount of substance in human gastric juice that can help digestion is hydrochloric acid. In hydrochloric acid, hydrogen is+1 and chlorine is-1, that is, the chemical formula is HCl. ..

(4) An acid often contained in soft drinks. Soft drinks are called carbonated drinks, so the acid they contain is carbonic acid, in which hydrogen is+1, carbonate is -2, and the chemical formula is H2CO3.

⑤ The substance used to treat hyperacidity, commonly known as baking soda, is sodium bicarbonate, where sodium is+1 and bicarbonate is-1, and the chemical formula is nahco3.

So, the answer is: ① CH 4; ② carbon monoxide; ③ hydrochloric acid; ④h2co 3； ⑤ Sodium bicarbonate.