Question

1.05 - test review - counting atoms
how many oxygen atoms are in the molecule, al₂(so₄)₃?
○ 4
○ 3
○ 12
○ 6

Explanation:

Step1: Analyze the formula structure

In the formula $\text{Al}_2(\text{SO}_4)_3$, the subscript outside the parentheses affects all atoms inside the parentheses.

Step2: Count oxygen atoms in one $\text{SO}_4$ group

In one $\text{SO}_4$ group, there are 4 oxygen atoms.

Step3: Multiply by the number of $\text{SO}_4$ groups

There are 3 $\text{SO}_4$ groups (from the subscript 3 outside the parentheses). So the total number of oxygen atoms is $4\times3 = 12$.

Answer:

12 (corresponding to the option "12")