Data:
Arsenic Molar Mass = 74,9216 ≈ 75 u (<span>atomic mass unit)</span>
Solving:
1 mole of arsenic → 75g ------------ 6,02*10²³ molecules
..................................X -------------- 1 molecule
6,02*10²³X = 75

C. a change of state. It can be a physical or a chemical state of change.
Given:
P = 123 kPa
V = 10.0 L
n = 0.500 moles
T = ?
Assume that the gas ideally, thus, we can use the ideal gas equation:
PV = nRT
where R = 0.0821 L atm/mol K
123 kPa * 1 atm/101.325 kPa * 10.0 L = 0.500 moles * 0.0821 Latm/molK * T
solve for T
T = 295.72 K<span />
Diffusion is the net movement of a substance, this is generally from a area of high concentration to low concentration, the particles will collide or 'bounce' off one another and by random movement, will eventually spread out till they are even.
Atomic number = 18 (Number of protons)
Mass number = 18 + 20 (Number of protons + neutrons)