17. Which of the following lists contains only elements and a reason why they are elements
C12, H2, Na, He - Substances are elements because they are pure.
H, O, NaCl, N2, CO2-Substances are elements because they
contain more than one chemical symbol
Kr, Ne, Ar, He - Substances are elements because they are all noble
gases.
F3, Os, Li, H-Substances are elements because they all have
chemical symbols.

geosphere and hydrosphere.

this is because the geosphere has to do with geological events, while the hydrosphere controls all water on earth.

the awnser is group 12

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