Describing black coles
Why can't astronomers take a picture of a black hole?

-Gravity is so strong that even light cannot escape a black hole.

-The nearest black hole is too far away to be seen.

-There is no way to detect the locations of black holes.

-Black holes are too large to photograph.

A)   Gravity is so strong that even light cannot escape a black hole.

Explanation:

the answer is c. nacl

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