White fumes appears because of formation of HCl on reaction with atmospheric moisture.
White fumes appears due to the formation of HCl gas. Anhydrous aluminium chloride is partly hydrolyzed by the moisture in the atmosphere and produces HCl gas. This HCl further combines with the moisture of the air and appears white fumes.
AlCl3 +3H2O --> Al(OH)3 +3HCl
Reaction of BF3 with NaH produces B2H6 At 450K following reaction happens
2BF3 + 6NaH --> B2H6 + 6NaF