Question

what type of chemical reaction is shown: $ce{h_{2} + cl_{2} -> 2 hcl}$
single replacement
synthesis
decompostion
double replacement

Explanation:

This reaction combines two simple substances ($\text{H}_2$ and $\text{Cl}_2$) into a single compound ($2\text{HCl}$), which matches the definition of a synthesis (combination) reaction. Single replacement involves one element replacing another, decomposition breaks a compound into simpler substances, and double replacement swaps ions between two compounds, none of which apply here.

Answer:

Synthesis