Molarity is a concentration unit, defined to be the number of moles of solute divided by the number of liters of solution.
Explanation:
Upon dissolution of KCl heat is generated and temperature of the solution raises.
Therefore, heat generated by dissolving 0.25 moles of KCl will be as follows.

= 4.31 kJ
or, = 4310 J (as 1 kJ = 1000 J)
Mass of solution will be the sum of mass of water and mass of KCl.
Mass of Solution = mass of water + (no. of moles of KCl × molar mass)
= 200 g + 
= 200 g + 13.625 g
= 213.625 g
Relation between heat, mass and change in temperature is as follows.
Q = 
where, C = specific heat of water = 
Therefore, putting the given values into the above formula as follows.
Q = 
4310 J =
Thus, we can conclude that rise in temperature will be
.
Answer: The missing coefficient is 2.
Explanation:
According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.

As in the products, there are 2 atoms of sodium, thus there will be 2 atoms of of sodium in the reactant as well. This will balance the number of hydrogen and oxygen atoms as well.
Thus the missing coefficient is 2.
I would say water; water is extremely polar, and this is why it can break one of the strongest bonds, ionic bonds. NaCl, as you probably know, is a salt, and dissolves in water. However, the ionic bond holding the Na+ and the Cl- is extremely strong; the boiling point of NaCl is at 1413 degrees celcius (water is at 100 degrees celcius). This means that it requires A LOT of energy to break the bond, but water is able to dissolve and break the bond very easily. It is very polar, so I would answer your question with water. And the bond connecting the H and the O is a covalent bond.