For a monopoly firm, if the profit-maximizing output level is Q and revenue-maximizing output level is R, then
Any of these can be true, depending on the context.
Revenue-maximizing output corresponds to MR=0 and profit-maximizing output corresponds to MR=MC. Since MC>0, MR curve cuts the MC curve first before cutting the quantity axis. Hence, for a monopoly firm, the profit-maximizing output is always less than the revenue-maximizing output or Q<R