Correct Answer - Option 2 : is double the number of green balls.

Colour of balls - red, green and yellow.

1. There are as many red balls as there are yellow balls.

Let us assume that the number of yellow balls is 'y'.

So, the number of red balls is also 'y'.

2. There are twice as many yellow balls as there are green ones.

The number of green balls = y/2

⇒ y = 2 × The number of green balls

⇒ The number of red balls = 2 × The number of green balls (From 1)

Clearly, the number of red balls is double the number of green balls.

Hence, ‘**is double the number of green balls**’ is the correct answer.