pyramidal, if you have a molecule kit, i would strongly recommend watching a video of someone using a kit explaining the different shapes and following along. It helps a lot!
I will use this conversion:
1m = 1000 mm => 1 = 1m / 1000mm
1 m = 100 cm=> 1 = 1m / 100cm
1m = 10 dm=> 1 = 1m / 10 dm
So,
B) 3.8 * 10^7 cm^3 = 3.8 * 10^7 cm^3 * [1m / 100cm]^3 = 38 m^3
C) 3.8 * 10^5 dm^3 * [1m / 10 dm]^3 = 380 m^3
D) 3.8 * 10^8 mm^3 * [1m / 1000 mm]^3 = 0.38 m^3
Now you can compare the four volumes and conclude which is the largest.
Answer: option C) 3.8 * 10^5 dm^3
Avodagros number i.e. 6.023 ×10^23