We’re being asked for the initial rate of the reaction (in mol∙L-1∙s-1) based on the graph given.
An instantaneous reaction rate is the rate at a particular moment in the reaction and is usually determined graphically and can be calculated as:
Δ[ ] = change in concentration
Δt = change in time
For the initial rate, we’ll look at the smallest time possible and determine the concentration at that time. The graph below has a 10-second increments.