Can b2h6 react with alkene to form trialkyborane or diborane actually splits like this b2h6 to form 2bh3

Honestly, I have no idea what you asked.

Does Diborane (B2H6) split into borane (BH3) like this : B2H6 to ➡️ 2BH3?

So if Dibroane is equivalent to borane so the mole ratio is not to be considered between them?

Yes, Diborane splits. B2H6 to ➡️ 2BH3?

So this means in a Hydroboration reaction its the formation of diborane first in the equation 3NaBH4 + 4BF3 according to this mole ratio BF3 was limiting so thats tge reactant that was used to find number of moles of diborane do we have to consider the mole rationin the formation of borane B2H6 ➡️2BH3 so we multiply the number of moles of B2H6 by 2?

yes

so that makes perfect sense thx