The amount of HCl required for one experiment - 13.5 µl the volume in terms of L - 13.5 x 10⁻⁶ L the volume of HCl available - 0.250 L since one experiment uses up - 13.5 x 10⁻⁶ L then number of experiments - 0.250 L / 13.5 x 10⁻⁶ L = 1.8 x 10⁴ times the experiment can be carried out 18000 times
It is 2.1 x 10^3 because your base number needs to be in between 1 and 10, and the number you are converting is non-decimal, so the exponent is positive. It is 10^3 because you are moving the decimal 3 places to the right
