manganese dioxide is required in the laboratory preparation of oxygen gas though it does not take part in reaction? why

The Manganese Dioxide doesn't take part in the chemical reaction because it is a catalyst, so it can only increase the rate of the reaction, not change the substances used.

if you have to make a general question and respond to your thoughts, then this isn't really a question someone can you on. read the passage, form your question, and answer using your thoughts. no one else can understand how you interpreted this text if you don't tell us.