Barium is an element that is primarily used in fireworks because of its distinct green colour while on the other hand, lead is used in electrical industries due to its unique properties. The ions of these elements can simply be identified when its insoluble salts get precipitated by any process.
Answer:
The steps with correct mechanism are given below:
C
1) CH₄(g) + Cl(g) → CH₃(g) + HCl(g) : This is a slow step.
The rate is given as: R1 = k₁[CH₄][Cl]
2) CH₃(g) + Cl₂(g) → CH₃Cl(g) + Cl(g): This is a fast step.
The rate is given as: Rate = k₂[CH₃][Cl₂]
∴ CH₄(g) + Cl₂(g) → CH₃Cl(g) + HCl(g)
Here, the slowest step will be the rate-determining step.
Answer:
3.14 grams of ammonium thiocyanate must be used to react completely with 6.5 g barium hydroxide octahydrate.
Explanation:

The balance chemical equation is :

Mass of barium hydroxide octahydrate = 6.5 g
Moles of barium hydroxide octahydrate = 
According to reaction, 2 moles of ammonium thiocyanate reacts with1 mole of barium hydroxide octahydrate. The 0.020635 moles of barium hydroxide octahydrate will react with:

Mass of 0.04127 moles of ammonium thiocyanate;

3.14 grams of ammonium thiocyanate must be used to react completely with 6.5 g barium hydroxide octahydrate