Answer: 4.
and 
Explanation:
a) The given reaction is 
As the mass on both reactant and product side must be equal:


As the atomic number on both reactant and product side must be equal:



b) 
Total mass on reactant side = total mass on product side
15 =15 + x
x = 0
Total atomic number on reactant side = total atomic number on product side
8 = 7 + y
y = 1

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Answer:
The rate at which the solute dissolves will increase.
Explanation:
If a solution is stirred, the rate at which a solute dissolves would increase substantially provided the solution is not yet saturated.
Stiring would cause more of the solution to come in contact with every part of the solute. It will increase the surface area of contact for the solution to act which will shoot up the rate of reaction. Stiring helps to bring solutes in solutions into a more close contact with the molecules or compounds of the medium.
All the members of a family of elements have the same number of valence electrons and similar chemical properties. The horizontal rows on the periodic table are called periods.