The important difference between political parties and interest groups is political parties are public and interest groups are private entities.
Option B
Explanation:
Political parties run elections and form governments while on the other hand interest groups are groups of people who have similar ideologies and objectives and are supporting/will support similar causes.
Political parties- Let's take an example of US: republican and democrats.
While interest groups are of people like “student unions, labour unions, and social groups” and there are various other interest groups who influence the thinking of masses into voting for political party candidate that can fulfil their objectives.