Is it good idea to run with your jacket on when temp is 25-30 degree celsius. I run 7.2K (will do 10K one day :] ) 5 times a week. Is it helpful in reducing weight.
There is a history of athletes training in sweat suits for weight loss, and in some very limited capacities it makes sense. As a fighter, you want to be as big and strong as possible for your weight class, but just barely in that weight class. As such, running around in a sweat suit is a good way to dump a few pounds of water if you're getting weighed in the day before a match.
So yes, you will "lose weight", but it is entirely water weight.
There some good answers on here pertaining to fat loss; I would encourage you to read them.
As user19362 said, choice of clothing is very important when you are exercising.
By wearing a jacket when the temperatures are elevated, your body will not dissipate heat as efficiently as it would if you were not wearing a jacket (sweating cools the body via evaporation, and you will be trapping the moisture under your jacket). This is not a good means for losing weight, although you may end up sweating more, you are losing water weight only, which is actually very important when you run - you need to stay hydrated! You could end up dehydrated, feeling faint, or suffer illnesses due to the heat.
If you are looking to lose weight by running, given your other posts on the matter, ensure that you are eating healthily during the day (all meals), and ensure that, by running, you are producing a daily calorie deficit (burning more than you are taking in) - this means your body will start to burn other fuel sources (stored fat/sugars etc). However, this is not a message to cut back the food you eat - ensuring you have good daily nutrition is paramount.
Do not be put off if you do not see results straight away - the loss of weight through exercise can be slow, but you need to stick at it to see results! All the best, I hope this has helped :)