Which of the following reactions is a synthesis reaction?

A) Cl2 + 2NaBr ⟶ Br2 + 2NaCl

B) 4H + O2 ⟶ 2H20

C) 2Na + 2H20 ⟶ 2NaOH + H2

D) C7H16 + 1102 ⟶ 7CO2 + 8H20

B) 4H₂ (g) + O₂ (g) ⟶ 2H₂O (l)

Explanation: Chemical reactions occur when compounds or elements combine to form new compounds or other elements. Chemical reactions may be classified into various types which include synthesis reactions, replacement reaction, decomposition reactions, and precipitation reactions among others. In our case, we were supposed to identify a synthesis reaction. Thus, we need to know what is a synthesis reaction. A synthesis reaction is a reaction that occurs when two elements or small compounds combine to generate a large compound. In this case, B is the choice that shows a synthesis reaction where hydrogen gas combines with oxygen gas to yield water.