How many dozens of particles of dust are in 2.45 grams if each dust particle has a mass of 2.51 x 10-4 grams?

To get the number of dozens, we will first calculate the number of particles in 2.45 grams and the divide the number of particles by 12 (as one dozen contains 12 particles).

We know that one particle has a mass of 2.51 x 10^-4 grams and we want to know the number of particles in 2.45 grams. We can simply use cross multiplication to calculate this as follows:
number of particle = (2.45 x 1) / (2.51 x 10^-4) = 9760.95 particles which will be considered as 9760 particles only (we count whole particles)
number of dozens = 9760 / 12 = 813 dozens

The answer is probably c. xylem