Answer:
Initial rate of the reaction when concentration of hydrogen gas is doubled will be
.
Explanation:

Rate law says that rate of a reaction is directly proportional to the concentration of the reactants each raised to a stoichiometric coefficient determined experimentally called as order.
Initial rate of the reaction = R = 
![R = k\times [N_2][H_2]^3](https://tex.z-dn.net/?f=R%20%3D%20k%5Ctimes%20%5BN_2%5D%5BH_2%5D%5E3)
![4.0\times 10^5 M/s=k\times [N_2][H_2]^3](https://tex.z-dn.net/?f=4.0%5Ctimes%2010%5E5%20M%2Fs%3Dk%5Ctimes%20%5BN_2%5D%5BH_2%5D%5E3)
The initial rate of the reaction when concentration of hydrogen gas is doubled : R'
![[H_2]'=2[H_2]](https://tex.z-dn.net/?f=%5BH_2%5D%27%3D2%5BH_2%5D)
![R'=k\times [N_2][H_2]'^3=k\times [N_2][2H_2]^3](https://tex.z-dn.net/?f=R%27%3Dk%5Ctimes%20%5BN_2%5D%5BH_2%5D%27%5E3%3Dk%5Ctimes%20%5BN_2%5D%5B2H_2%5D%5E3)
![R'=8\times k\times [N_2][H_2]^3](https://tex.z-dn.net/?f=R%27%3D8%5Ctimes%20k%5Ctimes%20%5BN_2%5D%5BH_2%5D%5E3)

Initial rate of the reaction when concentration of hydrogen gas is doubled will be
.
Answer:

Explanation:
Hello,
In this case, since the chemical reaction is:

We can see that hydrochloric acid and magnesium hydroxide are in a 2:1 mole ratio, which means that the neutralization point, we can write:

In such a way, the moles of magnesium hydroxide (molar mass 58.3 g/mol) in 500 mg are:

Next, since the pH of hydrochloric acid is 1.25, the concentration of H⁺ as well as the acid (strong acid) is:
![[H^+]=[HCl]=10^{-pH}=10^{-1.25}=0.0562M](https://tex.z-dn.net/?f=%5BH%5E%2B%5D%3D%5BHCl%5D%3D10%5E%7B-pH%7D%3D10%5E%7B-1.25%7D%3D0.0562M)
Then, since the concentration and the volume define the moles, we can write:
![[HCl]*V_{HCl}=2*n_{Mg(OH)_2}](https://tex.z-dn.net/?f=%5BHCl%5D%2AV_%7BHCl%7D%3D2%2An_%7BMg%28OH%29_2%7D)
Therefore, the neutralized volume turns out:

Best regards.
Hi the answer is actually B