All structures below have central atoms which would exceed the octet rule except for a. if3 b. nf3 c. sf4 d. brf3 e. brf4

b) NF3

Explanation:

the only structure that does not exceed the octet rule ( valence shell with 8 electrons)  is  NF3 . Knowing that

- N atom had originally 5 electrons in its valence shell

- F atom had originally 7 electrons in its valence shell

since each F atom has obtained 1 electron and completed its valence shell with 8 electrons ( from 7 electrons until 8 electrons) and N has also obtained 1 electron per each F bond, that is 3 electrons, summing up from 5 to 8 and thus also completing its valence shell with 8 electrons.

in a, c, d and e the central atom receives more electrons than the required to fill the p-orbital and accommodate them in the d-orbital

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