Which of these is considered a native element?
a. pyrite
b. galena
c. platinum
d. cinnabar

c. platinum

Explanation:

The native elements are elements that happend and synthethise naturally in nature, they basically happen and exist in pure form in nature and are divided into metals, semimetals and non metals, among this native elements we can find:

Metals

Platinum

Gold

Silver

Non metals

Sulfur and carbon

semimetals:

Bismuth and arsenic

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