Is investing in ETFs a good option for a long term? Say NIFTY BEES? Are they liquid enough?

Here is an article explaining the effect of the liquidity in the underlying stocks of an ETF on the ability of the market maker to keep the Bid/Ask in line with the value of the underlying basket of assets.

With respect to your question, there are two factors that I can highlight -

  1. The underlying equity basket in this case is top 50 stocks on the NSE which are likely to be always high in terms of liquidity.
  2. Whether you believe in the ability of the ETF sponsor/ Authorized Participant to perform their activity effectively.

Disclaimer - The article explains about ETF activity in US, there might be differences in how ETF’s operate in India. If so somebody else can expand on that.

This is a diagram on the NSE website explaining the structure of an ETF https://www1.nseindia.com/products/content/equities/etfs/structure_etf.htm