What are the maximum sprinkler number for 4" pi[e according to NFPA?(i dont mean the sprinkler to be installed direct on the 4" but on other branches)

4" pipe is up  to100 sprinkler according to NFPA

Do you mean Nos of sprinklers ?

Nos Of Spr = Total Area to be under the sprinkler / NFPA 13 X NFPA 14

the number of sprinklers related to the hazard classification so,

for light hazard4" pipe will serve area and it is more than sprinkler

for ordinary hazard4" pipe will serve up to sprinkler

Yes True. Up to100 Sprinkler heads can be installed with4" NPS.