By considering the reaction equation is:
5Br(aq)+BrO3(aq)+6H(aq)= 3Br2(aq)+3H2O(l)
when the average rate of consumption of Br = 1.86x10^-4 m/s
So from the reaction equation 
5Br → 3Br2 when we measure the average rate of formation (X) during the same interval So,
∴ 1.86x10^-4/5 = X / 3
∴X = 1.1 x 10^-4 m/s
∴the average rate of formation of Br2 = 1.1x10^-4 m/s
        
             
        
        
        
The order of the answers are as follows:
B
C
D
A
        
             
        
        
        
Answer: -
The experiment Niven is doing is burning of Mg.
The first step would be finding the molar mass of MgO
 Atomic mass of Mg = 24 g
Atomic mass of Oxygen = 16 g
Molar mass of MgO = 24 x 1 + 16 x 1 = 40 g
The balanced chemical equation for this reaction is
2 Mg + O2 -- > 2MgO
From the balanced equation we see that
2 Mg gives 2 MgO
2 x24 g of Mg O gives 2 x 40 g of MgO.
28g of MgO gives

 = 46.66 g of MgO.
 
        
                    
             
        
        
        
Hey there!:
Molar mass:
H2 = 2.01 g/mol    ;    H2O = 18.01
Given the reaction:
2 H2 + O2 = 2 H2O
2 * (2.01 ) g H2 ------------- 2 * ( 18.01 ) g H2O
mass H2 --------------------- 1.80 g H2O
mass H2 = 1.80 * 2 * 2.01 / 2* 18.01
mass H2 = 7.236 / 36.02
mass H2 = 0.2008 g
Hope that helps!