What is the difference of electronegativity of each bond of formaldehyde and ammonia?

Here's what I get  

Explanation:

1. Formaldehyde

C-H:  ΔEN = |2.55 - 2.20| = |0.35|  = 0.35

C-O:  ΔEN = |2.55 - 3.44| = |-0.89| = 0.89

2. Ammonia

N-H: ΔEN = |3.04 - 2.20| =|0.84| = 0.84

b. is the answer hoped i        

as given the equation is

2al + 6 hcl > 2 alcl3 + 3 h2(g)

as per equation two moles of aluminum reacts with six moles of hcl to give two moles of alcl3 and three moles of hydrogen gas

given: three moles of al are present and 7 moles of hcl

for three moles of aluminum nine moles of hcl will be required

however as 7 moles of hcl are present so the limiting reagent is hcl

hcl is going to decide the number of moles of product formed

when six moles of hcl are present = 3 moles of h2 are formed

when one mole of hcl is present == 3/6 mole sof h2 will be formed

when 7 moles of hcl are present = 3 x 7/ 6 moles of h2 will be formed = 3.5 moles of h2