my babies birth weight is 3.5 kg and at 1 and half his weight is 4.5 kgs is the weight gain of baby is good ?

A. Yup it is actually very good as a child has gained 1 kg in 1 1/2 month which is a healthy Vedha minimum expectation every month is about 500 g so child should have minimum gain 750 g after one and a half month where in your case it’s 1 KG which is very healthy