What are the differences between investing in index funds and contributing to a 401k plan for retirement savings?

Investing in index funds involves buying a diversified portfolio of stocks or bonds that track a specific market index, providing broad market exposure. Contributing to a 401k plan involves setting aside a portion of your salary in a tax-advantaged retirement account, often with employer matching contributions. Index funds offer passive investing with lower fees, while a 401k plan allows for tax benefits and potential employer contributions.