Answer:
1) Net ionic equation :

2) 0.765 M is the molarity of the carbonic acid solution.
Explanation:
1) In aqueous carbonic acid , carbonate ions and hydrogen ion is present.:
..[1]
In aqueous potassium hydroxide , potassium ions and hydroxide ion is present.:
..[2]
In aqueous potassium carbonate , potassium ions and carbonate ion is present.:
..[3]

From one:[1] ,[2] and [3]:

Cancelling common ions on both sides to get net ionic equation :

2)
To calculate the concentration of acid, we use the equation given by neutralization reaction:

where,
are the n-factor, molarity and volume of acid which is 
are the n-factor, molarity and volume of base which is KOH.
We are given:

Putting values in above equation, we get:

0.765 M is the molarity of the carbonic acid solution.