A student observes some firewood as it is heated and burns. The student concludes that a chemical reaction has occurred. Which of the following observations about the burning wood provides the best evidence of a chemical reaction? A. Heat is added to the firewood.
B. The wood change shape and size.
C. The temperature of the wood increases.
D. Gas is produced as the wood turns black.

not clear

the answer is:  

line graphs show patterns in data with variables that change over time; whereas, circle graphs show data as parts out of a whole (such as out of 100%).

catya your not at all which answer i've seen you do this on another question!

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