A chemical reagent that is used in this experiment is silver nitrate (AgNO3). It is used to distinguish calcium chloride and calcium carbonate. when this reagent is used, silver from silver nitrate reacts with Chloride to calcium chloride and forms silver chloride, making a precipitates of white color.
Answer : The pressure after the temperature change is, 0.752 atm
Explanation :
Gay-Lussac's Law : It is defined as the pressure of the gas is directly proportional to the temperature of the gas at constant volume and number of moles.

or,

where,
= initial pressure = 0.82 atm
= final pressure = ?
= initial temperature = 
= final temperature = 
Now put all the given values in the above equation, we get:


Thus, the pressure after the temperature change is, 0.752 atm
B. Mn + NiBr₂ → Ni + MnBr₂
Explanation:
The reaction that can be predicted of all is Mn + NiBr₂ → Ni + MnBr₂.
The activity series is used to predict the products of single displacement reactions.
The series ranks metals in order of their reactivity. Those higher up in the series are highly reactive metals. Those at the bottom are slightly to non-reactive metals.
For a single displacement reaction to occur, a metal higher up in the activity series displaces one that is lower in the series.
Reaction A will not occur, Ba is higher in the series
Reaction C will not occur, Pt and Au are unreactive
Reaction D will not occur as Zn is lower in the series
Mn is higher in the reactivity series and it will displace Ni from the solution.
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Chemical equation is the symbolic representation of chemical reactions.
Explanation
Chemical reactions are known as the reaction where two or more molecules or compounds react with each other leading to formation of product compounds along with either release or absorption of energy.
The symbolic representation of the processes occurring in a chemical reaction is termed as chemical equation.
The symbolic representation includes the reactants, products, external energy type and quantity of external energy and also about release of energy if occurs.
So the reactants are usually written in the left side of the chemical equation whereas on the right the products are written.
Both the sides are linked by a single headed arrow mark.
Some both the sides are linked by double heated arrow mark indicating the equilibrium chemical reaction.
Al3+ is cation due to its positve charge
N3- is an anion due to its negative charge