Conversion of area units?

1 hectare (HA) = 10000 square meters = 100 square kilometers
1 square meter = 100 square decimeter = 10000 square centimeter

In the 21st century, nanotechnology is widely used. Nanometer is the unit of length, 1 nanometer = 10-9 meters. Two sides of VCD disc are used to carve small pits by laser. It is known that the width of small pits is only 0.4 micron (1 micron = 10-6 meters). Try to use nanometer as the unit of length. (the results are expressed by scientific notation)

0.4 μ M / 1nm = (4 × 10-7m) / 10-9m = 0.4 × 10-7 - (- 9) = 4 × 102

What are the weight units?

Ton, kilogram, gram, milligram and so on, you can go to the encyclopedia to have a look, there is more authority!

At the same temperature and pressure, the ratio of density to molar mass of a gas
It is indicated by the sign of T, P

The answer is basically correct
But note: temperature and pressure are expressed in capital T and small P respectively
At the same temperature and pressure, only the same amount of material or the same volume of gas, its density ratio = molar mass ratio

Formula of density and relative density and formula of average molar mass under gas standard condition (2)

PV = NRT (basic)
PV=m/MRT
PM=ρRT

At the same temperature and pressure, the molar mass ratio of two gases is equal to the density ratio,

Correct, the molar mass ratio of two gases at the same temperature and pressure is equal to the density ratio, because the relative volume ratio of gas at the same temperature and pressure is fixed, so it is correct

Why is the molar mass ratio of two gases equal to the density at the same temperature and pressure

N = m / m, n = V / VM, P = m / V, so that we can eliminate the fact that the molar mass ratio equals the density

A. At the same temperature and pressure, the volume ratio of two gases is equal to the molar mass ratio B. at the same temperature and pressure, the mass ratio of two gases is equal to the density ratio

A is wrong
At the same temperature and pressure, the number of molecules in the same volume of gas is equal, so the volume ratio of two gases is equal to the mass ratio of their substances, independent of the molar mass
B is also wrong
At the same temperature and pressure, the density ratio of two gases is equal to the molar mass ratio, but has nothing to do with the amount of matter

How to calculate the molar mass when the gas density is known under the standard condition

4, we have to change the unit to g / mol

Proving the relationship between gas density and molar mass under standard condition
M=22.4*p(g/mol)

I think this formula is very easy to understand
M: Mass per mole of gas
22.4: volume per mole of gas
p: Density of gas
It is similar to the Formula M = PV

Conversion of area units?