How many grams of nacl are required to prepare 50ml of a 2.0 molar solution

5.85 gm.

Explanation:

We know that,

Normality = Molarity × Molecular weight

Equivalent weight

Since molecular weight of NaCl= equivalent weight = 23+35.5 =58.5

Normality of NaCl= molarity=2

Now,

Normality= weight in gram ×1000

Volume ×equivalent weight

Weight in gram is given by,

=Normality × Volume × equivalent weight

1000

= 2× 50 × 58.5

1000

=5.85 gm.

Single Keto group favors keto group over enol group due to following reason.

Unlike in beta-dicarbonyl compounds (which favors enol form) single keto group ketones are more stable in keto form.

For stability I searched for the bond energies. Below are the two forms. You can easily see the three different types of bonds and their energies. The main difference comes in the bond energy of C=O (carbonyl) group, which has the highest energy. Other energies are some what close to each other. 

Remember: Greater the bond energies, greater will be the stability of compound.

Result:
          The reason is "C=O bond is much stronger than C=C Bond".