Question

Which of the following best describes a single-replacement reaction?

Answer 1

Answer: B. One element takes the place of another in a compound.

Explanation:

Single replacement reaction is a chemical reaction in which more reactive element displaces the less reactive element from its salt solution.

Example: $Mg+2HCl\rightarrow MgCl_2+H_2$

Thus magnesium when dropped into an aqueous solution of $HCl$ releases hydrogen gas by replacing hydrogen from its position.

A. A compound breaks apart into separate elements: Decomposition

Example: $Li_2CO_3\rightarrow Li_2O+CO_2$ Double displacement reaction is one in which exchange of ions take place.  

B. One element takes the place of another in a compound: Single replacement

C. Two elements switch places in two compounds: Double displacement reaction

Example: $2NaOH(aq)+(NH_4)_2SO_4(aq)\rightarrow 2NH_4OH(aq)+Na_2SO_4(aq)$

D.  Two elements combine to form a compound: Synthesis reaction

Example: $2Mg+O_2\rightarrow 2MgO$  

Answer 2

Answer

B. One element takes the place of another in a compound

Explanation

A single-replacement reaction occurs when one element is substituted for another element in a compound.The  reacting materials are normally pure elements such as a metal or hydrogen gas with an aqueous compound.A new aqueous compound plus a different pure element are formed as products.