Explanation:

To find the number of girls in the class, we'll use the concept of weighted averages:

- The average age of all students is 22 years.

- The average age of boys is 26 years. There are 12 boys.

- The average age of girls is 19 years.

- Let the number of girls be $G$.

The equation for average age becomes:

$$\frac{(12\times 26)+(G\times 19)}{12+G}=22$$

Simplify:

$$312+19G=22(12+G)$$

$$312+19G=264+22G$$

$$312-264=22G-19G$$

$$48=3G$$

$$G=16$$

- Therefore, the number of girls is $\mathbf{\text{16}}$.

- Option 3 is correct.

The correct answer is Option: 3, 16.