Answer:
hydrogen
Step-by-step explanation:
The combination between chlorine and hydrogen forms an explosive reaction. In fact, chlorine and hydrogen combine according to the following equation:
![Cl_(2)_((g)) + H_(2)_((g)) = 2HCl_((g))](https://img.qammunity.org/2020/formulas/physics/middle-school/xt0qgccciw07rbybh6y9u944tzh37g0kz6.png)
The reaction, when it takes place in a solution, that is, with water, results in fuming hydrochloric acid.