**Calculating the Molar Mass of a Gas**

To calculate the molar mass of a gas, we need to know its density and the pressure at which it is measured. The molar mass can be determined using the ideal gas law equation, PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature.

In this case, we are given the density of the gas, which is 2×10 g/cm³, and the pressure, which is 1 atm. We can use these values to calculate the molar mass of the gas.

**Step 1: Convert Density to Molar Density**

First, we need to convert the density to molar density, which is the number of moles of gas per unit volume. The molar density (D) can be calculated using the formula:

D = (molar mass) / (molar volume)

where molar volume is the volume occupied by one mole of gas at a given temperature and pressure. The molar volume can be calculated using the ideal gas law equation:

PV = nRT

Rearranging the equation to solve for the molar volume, we have:

V = (nRT) / P

Substituting the given values, we have:

V = (1 mol * R * T) / P

Since the volume is given in cm³, we need to convert it to liters by dividing by 1000.

V = (1 mol * R * T) / (P * 1000)

**Step 2: Calculate the Molar Density**

Now, we can calculate the molar density by dividing the molar mass by the molar volume:

D = (molar mass) / (V)

**Step 3: Solve for the Molar Mass**

Finally, we can solve for the molar mass by rearranging the equation:

(molar mass) = (D) * (V)

Substituting the given values, we have:

(molar mass) = (2×10 g/cm³) * (V)

Remember to convert the density to g/L by multiplying by 1000, since the molar volume was expressed in liters.

(molar mass) = (2×10 * 1000 g/L) * (V)

**Step 4: Substitute the Molar Volume**

Substituting the expression for the molar volume, we have:

(molar mass) = (2×10 * 1000 g/L) * (1 mol * R * T) / (P * 1000)

Simplifying the equation, we get:

(molar mass) = (2×10 * R * T) / P

Now, we can calculate the molar mass using the given values for R, T, and P.