**Solution:**

When CH3COOH (acetic acid) reacts with NaOH (sodium hydroxide), a neutralization reaction occurs. The reaction equation is as follows:

CH3COOH + NaOH → CH3COONa + H2O

The balanced equation shows that one mole of CH3COOH reacts with one mole of NaOH to form one mole of water and one mole of sodium acetate (CH3COONa).

To find the pH of the resulting solution, we need to consider the dissociation of sodium acetate in water:

CH3COONa → CH3COO- + Na+

Since sodium acetate is a salt of a weak acid (CH3COOH), it undergoes hydrolysis in water. The acetate ion (CH3COO-) can accept a proton from water, resulting in the formation of hydroxide ions (OH-) and acetic acid (CH3COOH):

CH3COO- + H2O → CH3COOH + OH-

The hydroxide ions (OH-) produced by the hydrolysis of the acetate ion will react with the remaining acetic acid (CH3COOH) in the solution:

OH- + CH3COOH → CH3COO- + H2O

This reaction is a weak acid-base reaction between the hydroxide ions and acetic acid. The resulting solution will contain a mixture of acetic acid (CH3COOH), acetate ion (CH3COO-), and hydroxide ions (OH-).

**Buffer Solution:**

The resulting solution will act as a buffer because it contains a weak acid (CH3COOH) and its conjugate base (CH3COO-). A buffer solution can resist changes in pH when small amounts of acid or base are added.

The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation:

pH = pKa + log ([A-]/[HA])

Where pH is the solution's pH, pKa is the acid dissociation constant, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the weak acid.

In this case, the conjugate base is the acetate ion (CH3COO-) and the weak acid is acetic acid (CH3COOH). The pKa value for acetic acid is 4.8.

**Calculations:**

Given that 50 ml of 0.1M CH3COOH is mixed with 50 ml of 0.1M NaOH, the final volume of the solution is 100 ml.

The initial concentration of CH3COOH is 0.1M, which means that the concentration of acetic acid in the final solution is also 0.1M.

Since the initial concentration of NaOH is 0.1M, the concentration of hydroxide ions (OH-) in the final solution is also 0.1M.

Using the Henderson-Hasselbalch equation, we can calculate the pH of the resulting solution:

pH = 4.8 + log ([CH3COO-]/[CH3COOH])

Since the initial concentration of CH3COOH is 0.1M and the concentration of hydroxide ions (OH-) is 0.1M, the concentration of the acetate ion