Question

1. which of the following compounds would contain 6 atoms of oxygen? (3pts) □ ca(oh)₂ □ al₂(hpo₄)₃ □ co(no₃)₂ □ na₂cr₂o₇

Explanation:

Step1: Count O atoms in $\text{Ca(OH)}_2$

Each $\text{OH}^-$ has 1 O; 2 groups: $1\times2=2$ O atoms

Step2: Count O atoms in $\text{Al}_2(\text{HPO}_4)_3$

Each $\text{HPO}_4^{2-}$ has 4 O; 3 groups: $4\times3=12$ O atoms

Step3: Count O atoms in $\text{Co(NO}_3\text{)}_2$

Each $\text{NO}_3^-$ has 3 O; 2 groups: $3\times2=6$ O atoms

Step4: Count O atoms in $\text{Na}_2\text{Cr}_2\text{O}_7$

Direct count: $7$ O atoms

Answer:

$\boldsymbol{\text{Co(NO}_3\text{)}_2}$