Final answer:
The mass of a grain of sand given as 3.5 x 10^-10 kg is already in standard form.
Step-by-step explanation:
The mass of a grain of sand is approximately 3.5 x 10^-10 kg, which is already in standard form (standard form denotes a number as a coefficient between 1 and 10 multiplied by a power of 10). For questions asking about the volume of Avogadro's number of sand grains and the length of beach coverage, these represent applications of dimensional analysis in physics and material science, involving concepts of molarity and volume calculations. However, the initial query is simply asking for the confirmation that the expression of the grain of sand's mass is in standard form which, as stated, it indeed is.