Answer : The correct option is, (C) spontaneous only at low temperatures.
Explanation :
According to Gibb's equation:

= Gibbs free energy
= enthalpy change
= entropy change
T = temperature in Kelvin
As we know that:
= +ve, reaction is non spontaneous
= -ve, reaction is spontaneous
= 0, reaction is in equilibrium
The given chemical reaction is:

As we are given that, the given reaction is exothermic that means the enthalpy change is negative.
In this reaction, the randomness of reactant molecules are more and as we move towards the formation of product the randomness become less that means the degree of disorderedness decreases. So, the entropy will also decreases that means the change in entropy is negative.
Now we have to determine the spontaneity of this reaction when ΔH is negative and ΔS is negative.
As, 

(at high temperature) (non-spontaneous)
(at low temperature) (spontaneous)
Thus, the reaction is spontaneous only at low temperatures.
Answer: A. 28.6 ml of the 0.7 M solution we need to start with.
B. There are 0.02 moles of solute were in the 0.7 M solution.
C. Amount of water to be added is 21.4 ml
D. The resulting solution will have concentration of 0.28 M
Explanation:
According to the dilution law,
where,
= molarity of stock solution = 0.7 M
= volume of stock solution = ?
= molarity of diluted solution = 0.4 M
= volume of diluted solution = 50 ml
Putting in the values we get:
A. 28.6 ml of the 0.7 M solution we need to start with.
B. Molarity of a solution is defined as the number of moles of solute dissolved per liter of the solution.
where,
n = moles of solute
= volume of solution in ml

Thus there are 0.02 moles of solute were in the 0.7 M solution.
C. Amount of water to be added = (50-28.6 ) ml = 21.4 ml
D. If water added is 
If volume of concentrated solution will be more , the resulting solution will have lesser concentration of 0.28 M
Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions. Example : Reaction of iron nails with copper sulphate solution.
Answer:
C the mass of the reactant molecules is the same as the mass of the product
Answer:
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