**Calculating the Density of a Gas**

To calculate the density of a gas, we need to know its molecular weight, temperature, and pressure. In this case, we have a gas with a molecular weight of 78.1 g/mol, a pressure of 740 torr, and a temperature of 98 degrees Celsius. Let's break down the steps to calculate the density.

**Step 1: Convert the Temperature**

First, we need to convert the temperature from Celsius to Kelvin since the ideal gas law requires temperatures in Kelvin. To do this, we add 273.15 to the temperature in Celsius.

98 °C + 273.15 = 371.15 K

So, the temperature in Kelvin is 371.15 K.

**Step 2: Convert the Pressure**

Next, we need to convert the pressure from torr to atm since the ideal gas law uses pressure in atm. The conversion factor is 1 atm = 760 torr.

740 torr ÷ 760 torr/atm = 0.974 atm

So, the pressure in atm is 0.974 atm.

**Step 3: Calculate the Density**

The ideal gas law can be used to calculate the density of a gas using the formula:

Density = (molecular weight * pressure) / (gas constant * temperature)

The gas constant (R) is a constant value of 0.0821 L·atm/(mol·K).

Using the given values:

Density = (78.1 g/mol * 0.974 atm) / (0.0821 L·atm/(mol·K) * 371.15 K)

Simplifying the equation:

Density = (78.1 g * atm * K) / (mol * L * mol * K)

The units cancel out, leaving us with:

Density = 78.1 g / L

So, the density of the gas is 78.1 g/L.

**Conclusion**

The density of the gas with a molecular weight of 78.1 g/mol, at a pressure of 740 torr and a temperature of 98 degrees Celsius, is 78.1 g/L.

From eqn. P=dRT/M
d=PM/RT
d=.974×78.1/.082×371( 740torr=.974atm)
d=2.50g/L