"risk free interest rate" in Black Scholes In Black Scholes model r is defined as risk free interest rate. Could you please explain what is risk free? Is it same as interest rate on checking account?
Generally speaking, a risk-free rate refers to the yield you get on a government bond (read more here).

On a checking account there's a possibility that the bank would fail. Yes, it's FDIC insured, but up to \$250K.