Reflection of P(a, b) in y-axis followed by reflection in x-axis is :

1. (-a, b)

2. (a, -b)

3. (-a, -b)

4. (a, b)

We know that,

On reflecting in y-axis the sign of x co-ordinate changes.

Let on reflection in y-axis point P(a, b) becomes P'.

P(a, b) ⇒ P'(-a, b).

We know that,

On reflecting in x-axis the sign of y co-ordinate changes.

Let on reflection in x-axis point P'(-a, b) becomes P".

P'(-a, b) ⇒ P"(-a, -b).

Hence, Option 3 is the correct option.