Answer: Second and fourth pairs of rectangle are similar.
Explanation: Since, If two Shapes are similar then the ratios of their corresponding sides are equal.
In First figure ratios of corresponding sides are not equal.
Because,
≠ 
Therefore, they are not similar.
In second figure ratios of corresponding sides are equal.
Because,
= 
Therefore, they are similar.
In third figure ratios of corresponding sides are not equal.
Because,
≠ 
Therefore, they are not similar.
In fourth figure ratios of corresponding sides are equal.
Because,
=
Therefore, they are similar.