2) which of the following is a synthesis reaction?
(1) cu + 2agno3 → cu(no3)2 + 2ag
(2) 2cu +02→ 2cuo
(3) cucoo3 → cuo + co2
(4) cuo + h2 → cu + h2o

(4) CuO + H₂ → Cu + H₂O.

Explanation:

(1) Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag.

It is considered as a single replacement reaction that Cu replaces Ag in its salt AgNO₃.

(2) 2Cu + O ₂ → 2CuO.

It is a combustion reaction that Cu reacts with oxygen results CuO.

(3) CuCO₃ → CuO + CO₂.

It is a decomposition reaction that CuCO₃ is decomposed to CuO and CO₂.

(4) CuO + H₂ → Cu + H₂O.

It is considered as a synthesis reaction that two reactants CuO and hydrogen are reacted to produce Cu and H₂O.

So, the right choice is: (4) CuO + H₂ → Cu + H₂O.

< > according to newton's third law of motion, forces always act in equal but opposite pairs. another way of saying this is for every action, there is an equal but opposite reaction.< >