# What is the pressure less than $1$ $atm$ ?

A.At a place where water boils at $110{}^\circ C$

B.At a place where water boils at $90{}^\circ C$

C.At a place below sea level

D.At a place where water boils at $100{}^\circ C$

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**Hint:**Pressure is the physical force that is exerted on an object. It is defined as the force applied by the particles due to their collision with the walls of the container or due to particles colliding with each other.

**Complete step by step answer:**

Before talking about the answer, we should know about the ideal gas. It is a theoretical concept. It helps to predict the behavior of real gases. Ideal gas molecules do not attract or repel each other, only elastic collision takes place between them.

There is an ideal gas law, which states that pressure, temperature and volume are interrelated with each other. Illustrating further, it can be written as,

$PV=nRT$

where $P$ is the pressure, $V$ is the volume occupied by the gas, $T$ is the temperature of the gas, $n$ is the number of moles and $R$ is the gas constant.

Here, the answer to the question depends upon the ideal gas, that is

$PV=nRT$

We can say that $P\propto T$, that means, if pressure is increased, temperature also increases and if pressure is decreased, temperature also decreases.

As we know that water boils at $373K$ with atmospheric pressure of $1atm$ .

If the pressure is higher than $1atm$ , then the temperature of water will be more than $373K$ and if the pressure is lesser than $1atm$ , then the temperature of water will be less than $373K$

The pressure less than $1atm$ is at a place where water boils at $90{}^\circ C$ .

**So, the correct option is (B), at a place where water boils at $90{}^\circ C$ .**

**Note:**

Atmospheric pressure $(atm)$ is defined as the unit of pressure of where

$1atm=101325Pa$

And $0{}^\circ C=273K$

$100{}^\circ C=373K$

So, ${{T}_{k}}={{t}_{c}}+273$, where ${{T}_{k}}$ is temperature in Kelvin and ${{t}_{c}}$ is temperature in Celsius.