Passive investing is the approach of investment in which the investor will be trying to replicate the index and we will be trying to form a Portfolio with the index or he will be investing into the index form as he believe in the Efficient market hypothesis and he believes that he cannot make abnormal return.

Active investment is a type of investment in which investor will be continuously synchronising his portfolio in respect to the market changes and he wants to maximize his rate of return and make up normal rate of return as he do not believe in Efficient market hypothesis and he wants to maximize upon the price discrepancies.

Passive investing is becoming more popular because it is providing with higher rate of return and it is providing with stable rate of return because most of the active funds are not able to outperform the passive funds.

yes, passive investing is important for market efficiency because market efficiency advocates only for passive investment.

It will be useful to explain the types of market efficiency because Efficient market will always advocate for discounting of all the information into the market and one can never beat the market rate of return whereas passive investment will also believe the same and invest into the market for replicating the market rate of return.