Hi Neelam,
I'm with you, mosquitos can be quite annoying. The only "natural" remedy I've found is Winter, they don't seem to like the cold ;) I do use a spray on my horses that works somewhat: Chamomile tea, citronella, lavendar, tea tree, apple cider vinegar and water. I never tried it on anything else. Let us know if you find something that works!

I have read that a good mosquito repellent is a solution of:
1 tsp soybean oil
1/4 tsp Palmolive liquid soap (does this disqualify it from being natural?)
1 cup water

with the soybean oil being the active ingredient. The article said it can be sprayed in the yard but I do not remember how long it lasts, maybe 3 hours? I have not yet tried it as I just found out about it, but I have tried STING FREE from Gardens Alive which has soybean oil as the active ingredient and it has worked for me (the label says it lasts 3 hours).