Can one build 4kg in muscle mass in two month's

If you added some more details about your figures it might have been helpful.  Theoretically you can , if you work out correctly and maintain  a high  protein diet, and maybe add a few nutritional supplements . It might take you longer then two months but if you work hard you'll do it. Unless you are very thin and thats a problem.

I think the bottom line is that you can (depending also on your current size) but remember, your diet is just as important as your training. If you won't eat enough high protein foods or intake enough calories, then you won't gain muscle mass.

yeh sure, depending on there size genes, training - how you train and what muscle groups you focus on, sleep, what they eat, and also how long they have been lifting weights for etc. (most probably a meso or endo type body, eating sleeping training all correctly and in timing), most probably with supplements or roids... (do not reccommend taking roids, too many health issues/concerns - i will never try this) 




somewhat fast improvement is like: started curling 10kgs bicep curls, after 3 months curling 22.5kgs....

increase = 12.5kgs 3 months

my bottom ribs are visible also my sternum,how can i cover them with muscle and how long wil it take?(I weigh 73 kilos and am about 15% body fat and i am 6'2 how long wil it take me to put on 12 kgs of muscle?)

how can i gain muscle mass in 1 month

how can i gain muscle mass in 1moth by weight lifting

Yes, one can.  It requires two main ingredients: progressive resistance exercise to muscle exhaustion on every set and a well-balanced diet that includes at least .8 gram of protein per pound of body weight per day and enough calories to increase body mass.  That is a simplification of a process involving many details, but that's the essence of it.  I had a woman trainee who gained 12 pounds of muscle (and lost 10 pounds of fat) in 8 weeks. 

It is possible to