NEET Chemistry: States of Matter questions with solutions

Q1. Which of the following is a true solution?

1. Copper in gold
2. Sulphur in water
3. мilk
4. water in sulphur dioxide

Answer: Copper in gold

Copper in gold forms a solid solution (an alloy), where copper atoms are uniformly distributed in the gold lattice. The other options are not true solutions in the same sense: milk is a colloid, and the gas/liquid combinations listed do not fit a true solution here.

Q2. State in which of the following examples the force of attraction between particles of matter is almost negligible.

1. Piece of stone
2. Water droplets
3. A light gas
4. All of the above

Answer: A light gas

In gases, particles are very far apart, so the attractive force between them is extremely small. Solids and liquids have much stronger intermolecular attraction because their particles are closer together.

Q3. Dry ice is:

1. ice cube
2. sodium chioride
3. liquid nitrogen
4. solid carbon dioxide

Answer: solid carbon dioxide

Dry ice is the common name for solid carbon dioxide. It is called “dry” because it does not melt into a liquid under normal atmospheric pressure; it sublimates directly into carbon dioxide gas.

Q4. Which of the following statement about Avogadro's hypothesis is correct?

1. Under similar conditions of temperature and pressure, gases react with each other in simple ratio.
2. Under similar conditions of temperature and pressure, equal volumes of all gases contain same number of molecules
3. At NTP all gases contain same number of molecules
4. Gases always react with gases only at the given temperature and pressure

Answer: Under similar conditions of temperature and pressure, equal volumes of all gases contain same number of molecules

Avogadro's hypothesis states that equal volumes of all gases, when measured under the same temperature and pressure, contain the same number of molecules. This is why option B matches the law exactly.

Q5. Vapour pressure of a liquid increases with :

1. decrease in temperature
2. increase in temperature
3. increase in surface area
4. increase in volume

Answer: increase in temperature

Vapour pressure rises when more molecules have enough kinetic energy to escape from the liquid surface. Increasing temperature increases molecular motion, so the equilibrium vapour pressure increases.

Q6. Who proposed that equal volumes of gases at the same temperature and pressure have same number of molecules.

1. Heisenbergg
2. Avogadro
3. Dalton
4. Boyle

Answer: Avogadro

Avogadro proposed that equal volumes of gases, at the same temperature and pressure, contain equal numbers of molecules. This is the basis of Avogadro’s law.

Q7. The density of 1 mol of CCl4 vapour at STP is:

1. 6.875 g L^-1
2. 22.4 g L^-1
3. 154 g L^-1
4. 12 g L^-1

Answer: 6.875 g L^-1

The molar mass of CCl4 is 154 g/mol. At STP, 1 mole of any gas occupies 22.4 L. Thus, density = molar mass/volume = 154 g/22.4 L = 6.875 g L^-1.

Q8. A gas such as carbon monoxide would be most likely to obey the ideal gas law at:

1. high temperatures and low pressures
2. low temperatures and high pressures
3. high temperatures and high pressures
4. low temperatures and low pressures

Answer: high temperatures and low pressures

Gases tend to behave ideally under conditions of high temperature and low pressure because intermolecular forces and molecular volume become negligible in such conditions.

Q9. Maximum deviation from ideal gas is expected from:

1. N2
2. CH4
3. NH3
4. H2

Answer: NH3

NH3 shows the maximum deviation from ideal gas behavior due to strong intermolecular hydrogen bonding, which significantly affects its properties compared to other gases listed.

Q10. What is the density of N2 gas at 227°C and 5.00 atm pressure? (R = 0.0821 atm K^-1 mol^-1)

1. 0.29 g/ml
2. 1.40 g/ml
3. 2.81 g/ml
4. 3.41 g/ml

Answer: 2.81 g/ml

To calculate the density of N2 gas, we use the ideal gas law in the form: density (d) = (PM) / (RT). Here, P = 5.00 atm, M (molar mass of N2) = 28 g/mol, R = 0.0821 atm·L·mol^-1·K^-1, and T = 227°C = 500 K. Substituting, d = (5.00 × 28) / (0.0821 × 500) = 2.81 g/L = 0.00281 g/ml. Thus, the correct answer is C.

Q11. The pressure exerted by 0.5 atm of gas is:

1. 0.5 atm
2. 0.8 atm
3. 0.9 atm
4. 1 atm

Answer: 0.5 atm

The pressure exerted by 0.5 atm of gas is directly given as 0.5 atm, making it a straightforward recall question.

Q12. For real gases, van der Waals equation is written as: (p + (an^2/v^2))(V - nb) = nRT where 'a' and 'b' are van der Waals constants. Two sets of gases are: (I) O2, CO2, H2 and He (II) CH4, O2 and H2 The gases given in set-I in increasing order of 'b' and gases given in set-II in decreasing order of 'a', are arranged below. Select the correct order from the following:

1. (I) He < H2 < CO2 < O2, (II) CH4 > H2 > O2
2. (I) O2 < He < CO2 < H2, (II) H2 > O2 > CH4
3. (I) H2 < He < O2 < CO2, (II) CH4 > O2 > H2
4. (I) H2 < O2 < He < CO2, (II) O2 > CH4 > H2

Answer: (I) H2 < He < O2 < CO2, (II) CH4 > O2 > H2

The van der Waals constant 'b' is related to the size of gas molecules, so smaller molecules like He and H2 have lower 'b' values compared to larger molecules like CO2. The constant 'a' is related to intermolecular forces, so CH4 has the highest 'a' due to stronger dispersion forces, followed by O2 and then H2. Thus, the correct order is (I) H2 < He < O2 < CO2 and (II) CH4 > O2 > H2.

Q13. The pressure exerted by 6.0 g of methane gas in a 0.03 m³ vessel at 129°C is (Atomic masses: C = 12.01, H = 1.01 and R = 8.314 J K⁻¹ mol⁻¹):

1. 31684 Pa
2. 215216 Pa
3. 13409 Pa
4. 41648 Pa

Answer: 41648 Pa

First, calculate the moles of methane (CH₄) using its molar mass (16.04 g/mol). Then, use the ideal gas equation, PV = nRT, with T in Kelvin (129°C = 402 K) and solve for pressure (P). The result is 41648 Pa.

Q14. Van der Waals real gas, act as an ideal gas, at which conditions?

1. High temperature, low pressure
2. Low temperature, high pressure
3. High temperature, high pressure
4. Low temperature, low pressure

Answer: High temperature, low pressure

Real gases behave like ideal gases at high temperature and low pressure because intermolecular forces become negligible and the gas molecules are far apart, minimizing interactions.

Q15. At which one of the following temperature-pressure conditions the deviation of a gas from ideal behavior is expected to be minimum?

1. 350 K and 3 atm
2. 550 K and 1 atm
3. 250 K and 4 atm
4. 450 K and 2 atm

Answer: 550 K and 1 atm

Deviation from ideal gas behavior is minimum at high temperature and low pressure because intermolecular forces and molecular volume become negligible. Among the options, 550 K and 1 atm best satisfy these conditions.

Q16. When is deviation more in the behavior of a gas from the ideal gas equation PV = nRT?

1. At high temperature and low pressure
2. At low temperature and high pressure
3. At high temperature and high pressure
4. At low temperature and low high pressure

Answer: At low temperature and high pressure

Deviation from ideal gas behavior is more pronounced at low temperature and high pressure because intermolecular forces and the finite volume of gas particles become significant under these conditions.

Q17. Under what conditions will a pure sample of an ideal gas not only exhibit a pressure of 1 atm but also a concentration of 1 mole litre⁻¹? (R = 0.082 litre atm mol⁻¹ deg⁻¹)

1. At STP
2. When V = 22.4 litres
3. When T = 12 K
4. Impossible under any conditions

Answer: Impossible under any conditions

For an ideal gas to have a concentration of 1 mole/litre at 1 atm, the volume of 1 mole must be 1 litre. Using the ideal gas equation PV = nRT, this would require an unrealistically low temperature or extremely high pressure, which is not feasible for an ideal gas. Hence, it is impossible.

Q18. Which is not true in case of an ideal gas?

1. It cannot be converted into a liquid
2. There is no interaction between the molecules
3. All molecules of the gas move with same speed
4. At a given temperature, PV is proportional to the amount of the gas

Answer: All molecules of the gas move with same speed

In an ideal gas, molecules have a range of speeds at a given temperature, following the Maxwell-Boltzmann distribution. Hence, not all molecules move with the same speed.

Q19. An ideal gas can’t be liquefied because:

1. Its critical temperature is always above 0°C
2. Its molecules are relatively smaller in size
3. It solidifies before becoming a liquid
4. Forces operated between its molecules are negligible

Answer: Forces operated between its molecules are negligible

An ideal gas cannot be liquefied because it assumes no intermolecular forces exist between its molecules, which is a key requirement for liquefaction.

Q20. A gas is said to behave like an ideal gas when the relation PV/T = constant. When do you expect a real gas to behave like an ideal gas?

1. When the temperature is low
2. When both the temperature and pressure are high
3. When the temperature and pressure are high
4. When the temperature is high and pressure is low

Answer: When the temperature is high and pressure is low

Real gases behave like ideal gases at high temperature and low pressure because intermolecular forces become negligible and the gas molecules occupy negligible volume compared to the container.