Q1: Which one can be directly solidified from gaseous state wihtout entering into liquid state ?

ANS:C - Carbon dioxide

Helium can be directly solidified from the gaseous state without entering into a liquid state under standard atmospheric pressure. This process is known as "deposition" or "deposition from the gas phase." At extremely low temperatures, close to absolute zero (-273.15°C or 0 Kelvin), helium gas can be solidified directly into solid helium without passing through a liquid phase. This phenomenon occurs due to the unique properties of helium at low temperatures, where it exhibits superfluidity and undergoes a phase transition directly from gas to solid. Oxygen and carbon dioxide both undergo a phase transition from gas to liquid before solidification under standard atmospheric pressure and temperature conditions. Therefore, helium is the only option among the given choices that can be directly solidified from the gaseous state without entering into a liquid state.