Answer:- HBr is limiting reactant.
Solution:- The given balanced equation is:

From this equation, There is 2:6 mol or 1:3 mol ratio between Al and HBr. Since we have 8 moles of each, HBr is the limiting reactant as we need 3 moles of HBr for each mol of Al.
The calculations could be shown as:

= 24 mol HBr
From calculations, 24 moles of HBr are required to react completely with 8 moles of Al but only 8 moles of it are available. It clearly indicates, HBr is limiting reactant.
The 2nd one I believe
Answer- 2nd
Answer:
Taq polymerase is a thermostable which states that it can even work at higher temperature. The main function of using this enzyme is that it is used to amplify the DNA which will help in producing ample amount of DNA sample.
The enzyme activity is temperature dependent. The denaturation and annealing steps of the PCR occurs at very high temperature.
Any other enzyme used at such an high temperature would have decreased the enzyme activity and the procedure would not be completed.
Answer:
Option A.
Lower air pressure results in a lower boiling point
Explanation:
This is because in an open system, the lower the pressure the lesser the energy that will be required for boiling point. The is little or no collision of air molecules with the surface of the liquid
But if there is increase in pressure, more energy will be required to get to boiling point because there will be strong collision between air molecules and surface of the liquid.