Question

which metal would not displace gold, au, from a compound?
copper, cu
potassium, k
magnesium, mg
none of them
identify the type of chemical reaction given here: c₂h₄(g) + 3o₂(g) → 2co₂(g) + 2h₂o(g)
synthesis
decomposition
complete combustion
incomplete combustion
classify the following reaction: mg(oh)2 + 2hno3 ------->mg(no3)2 + 2h2o
synthesis
decomposition
single displacement
double displacement

Explanation:

Step1: Recall metal - activity series

In the metal - activity series, a more reactive metal can displace a less reactive metal from its compound. Gold is a very less reactive metal. Potassium and magnesium are highly reactive metals and can displace gold. Copper is also more reactive than gold in terms of metal - displacement reactions. So, none of these metals would not displace gold.

Step2: Identify reaction type of $C_{2}H_{4}+3O_{2}

ightarrow2CO_{2}+2H_{2}O$
A complete combustion reaction of a hydrocarbon produces carbon dioxide and water. Here, ethylene ($C_{2}H_{4}$) reacts with oxygen to form carbon dioxide and water, which is a complete combustion reaction.

Step3: Identify reaction type of $Mg(OH)_{2}+2HNO_{3}

ightarrow Mg(NO_{3})_{2}+2H_{2}O$
In a double - displacement reaction, the positive and negative ions of two ionic compounds exchange places. Here, the $Mg^{2 + }$ ion from $Mg(OH)_{2}$ and the $H^{+}$ ion from $HNO_{3}$ exchange places with the $OH^{-}$ ion from $Mg(OH)_{2}$ and the $NO_{3}^{-}$ ion from $HNO_{3}$ respectively.

Answer:

1. D. none of them
2. C. complete combustion
3. D. double displacement