Answer:- 448 mL of hydrogen gas are formed.
Solution:- It asks to calculate the volume of hydrogen gas formed in milliliters at STP when 0.020 moles of magnesium reacts with excess HCl acid. The balanced equation is:

There is 1:1 mol ratio between Mg and hydrogen gas. So, the moles of hydrogen gas is also equals to the moles of Mg reacted.
moles of Hydrogen gas formed = 0.020 mol
At STP, volume of 1 mol of the gas is 22.4 L. We need to calculate the volume of 0.02 moles of hydrogen gas.

= 0.448 L
They want answer in mL. So, let's convert L to mL using the conversion formula, 1L = 1000mL

= 448 mL
So, 0.020 moles of magnesium would produce 448 mL of hydrogen gas at STP on reacting with excess of HCl acid.
Answer:
C. It may act as an insulator or a conductor.
Explanation:
Group B are the metalloids, so they have properties of both metals and nonmetals.
Answer:The equilibrium constant for a given reaction is [concentration of products]/[concentration of reactants].
Explanation:
Equilibrium constant=[concentration of products]/[concentration of reactants]
The concentration of reactant molecules is maximum at time 0 and it decreases as the reaction proceeds, The concentration of product molecules increases.At equilibrium the concentration of reactants and products are equal.
All the changes would occur in accordance with the LeChateliers principle.
For the given reaction the following changes would occur:
a When CO is removed from the reaction mixture so the reaction would shift towards right that is in forward direction as we are decreasing the concentration of CO so the system would try to increase the concentration of CO and that can happen by more production of CO.
b Since the above reaction is an endothermic reaction so when we would be adding heat to the system that is when we would increase the temperature the reaction would shift forwards as more heat energy is absorbed by reactants to form more products.
c When more CO₂ is added so more amount of reactants are added to the system so the system would try to decrease the amount of reactants that is CO₂ and hence more amount of products would be formed.The reaction would shift in forward direction.
d Since this reaction is endothermic in nature so when we remove the heat from reaction hence even less amount of heat is present in the system and so the reaction shift in backward direction as the reaction cannot proceed without enough amount of heat.
In the problem, we are tasked to solved for the amount of carbon (C) in the acetone having a molecular formula of C 3 H 6 O. We need to find first the molecular weight if Carbon (C), Hydrogen (H), Oxygen (O).
Molecular Weight:
C=12 g/mol
H=1 g/mol
O=16 g/mol
To calculate for the percent by mass of acetone, we assume 1 mol of acetone.
%C=

%C=62.07%
Therefore, the percent by mass of carbon in acetone is 62.07%