Explore topic-wise InterviewSolutions in .

The CORRECT answer is (a) True

To explain I WOULD SAY: Viscosity is defined as the resistance to the flow of a liquid. It opposes a liquid’s layer movement with respect to one another. So, the above statement: the higher the viscosity, the slower the liquid FLOWS is true.

Correct answer is (b) ZERO

To explain I would SAY: The SURFACE tension in liquids decreases with RISE in temperature. As surface tension decreases, molecules become more active when temperature increases and surface tension becomes zero at critical temperature TC.

Right option is (c) Surface TENSION

For explanation I WOULD say: Surface Tension is the tendency of a fluid to OCCUPY least surface area as possible. It is defined as the force per UNIT distance. So, the spherical shape that is acquired by a WATER drop is due to surface tension.

The correct answer is (b) C = A

For EXPLANATION: When the angle of contact between the liquid and container is 90 degrees then the cohesive and adhesive FORCES in a liquid are equal. Cohesive force is the ATTRACTION between SIMILAR atoms and adhesive between different atoms.

Right CHOICE is (a) laminar flow

To explain I would say: The type of flow in LIQUIDS when each path flows in a different path, that do not INTERFERE with each other is laminar flow. At any point in the fluid, the VELOCITY of a fluid is constant is a CHARACTERISTIC of laminar flow.

The correct choice is (c) Newton/meter

Explanation: Surface Tension is the TENDENCY of a FLUID to occupy least surface AREA as possible. It is defined as the force per unit DISTANCE. So, the units of surface tension are Newton/meter in S.I. the SYSTEM, Dyne/cm in C.G.S system.

The CORRECT choice is (d) 0.25 dz/du

To explain I WOULD say: The formula of force required to maintain the flow of LAYERS is given by the formula F = ηAdu/dz, where η is the coefficient of viscosity, A is the area of contact and du/dz is the velocity GRADIENT. So by substituting we get an ANSWER as0.25dz/du.

Right choice is (a) Increases

The EXPLANATION: As there is a RISE in TEMPERATURE the viscosity of liquid increases while the viscosity of gas DECREASES. In liquids, due to rise in temperature, molecules have high thermal ENERGY so the can overcome intermolecular attractions.

Right option is (a) 0.1 kgm^-1s^-1

To explain I WOULD say: Poise is the unit of viscosity. It’s S.I. unit is 1 Newton second per square meter. It’s Pascal second. In C.G.S. system, the unit of viscosity is poise that is named after a SCIENTIST Jean Louise

Poiseuille. So, it’s 1 poise = 0.1 kgm^-1s^-1.

Correct CHOICE is (c) Van DER WAAL boiling point

For EXPLANATION I would say: The boiling point at pressure 1 atm is known as normal boiling point. Normal boiling point is slightly greater than the STANDARD boiling point as molecules change into the vapor phase and density of vapor increases.

The correct option is (a) a/Rb

The best explanation: Boyle’s TEMPERATURE Tb is given a/Rb, where a and b are the VAN der Waal’s constants for PRESSURE and volume correction. The temperature TILL which a GAS behaves like an ideal gas is Boyle’s temperature.

Correct OPTION is (d) 7.09 m^3

The best I can explain: From VAN der WAAL’s equation (P – an^2/V^2)(V – NB) = nRT, we know that V = b/NA = 42.69 x 10^-6m^3/mol/6.023 x 1023 molecules/mol. That equals 7.09 m^3/molecule. So the volume of a molecule is 7.09m^3.

Correct answer is (b) 23.71 x 10^-6 m^3/MOL

The best explanation: From van der Waal’s equation (P – an^2/V^2)(V – NB) = nRT, we have that UNITS of VOLUME and number of moles x b are same. So L = mol x b; units of b is L/mol otherwise can be written as m^3/mol.

The CORRECT choice is (a) vapor

Explanation: At critical temperature liquid state changes into gaseous state continuously the surface that SEPARATES both this state DISAPPEARS and gas below critical temperature can be liquefied by applying PRESSURE and this is called vapor of the SUBSTANCE.

Right CHOICE is (d) both gas and liquid

The explanation: A fluid is a gas or liquid that can be used to recognize the continuity. The fluid is SOMETHING deforms under shear stress APPLICATION and flows from ONE place to ANOTHER, it is also a subset of States of matter.

Correct option is (a) 8/27

To elaborate: The maximum TEMPERATURE gas can remain LIQUID is known as critical temperature. The temperature till which a gas behaves like an IDEAL gas is Boyle’s temperature. Boyle’s temperature TB is given by a/Rb critical temperature TC is given by 8a/27Rb. So the RATIO is 8/27.

The correct option is (b) 30.98-degree centigrade

Easy explanation: The critical temperature of carbon DIOXIDE is a MAXIMUM temperature where the carbon dioxide can remain as a LIQUID below this temperature. The carbon dioxide is GAS so the critical temperature for Carbon dioxide is 30.98 degrees centigrade.

Correct option is (c) 0.5081

The best explanation: Compressibility FACTOR Z = PV/nRT; Z = 50 ATM x (500/1000) ml / 2 x 0.082 x 300 K = 25/6×8.2 = 0.5081. That means Z < 1, so this is a negative deviation from ideal gas behaviour. So the gas is more compressible than expected.

Correct choice is (a) L/mol

To explain: The ideal GAS equation is given as (P – an^2/V^2)(V – nb) = nRT.So by CONSIDERING the equation, we can understand that the units of the volume are equal to the units of a number of moles X be so the units of b. So b’s units = volume / number of moles so it is L/mol.

The correct OPTION is (a) positive

Explanation: Above Boyle temperature, the value of the compressibility factor is greater than 1. So the gases show positive deviation from IDEAL gases as the forces of ATTRACTION between the gas molecules are very LOW.

The correct answer is (d) (P – an^2/V^2)(V – nb) = nRT

To explain I would say: (P – an^2/V^2)(V – nb) = nRT; where p is PRESSURE, a is the magnitude of intermolecular attractive forces within a gas, N is the number of moles, v is volume, B is a VAN der Waal constant, R is the universal gas constant and T is temperature.

Right choice is (a) Boyle temperature

To elaborate: The temperature at which a REAL gas obeys Boyle’s law and other ideal gas law at a CERTAIN range of pressure is called Boyle temperature or Boyle POINT. It is unique for every gas and depends upon its NATURE.

The correct answer is (B) low pressure

Explanation: At low-pressure conditions, Z = 1 handset BEHAVES as an ideal GAS but at high-pressure Z is GREATER than 1 and for intermediate pressure that is less than 1. So at low-pressure condition, a REAL gas behaves as an ideal gas.

Right option is (a) COMPRESSIBILITY factor

The explanation: PV/nRT is known as compressibility factor and is represented by the letter Z. It is a RATIO of PV and nRT; where p is pressure, V is VOLUME, n is the number of moles, R is the universal gas constant and T is TEMPERATURE.

Right answer is (b) false

The best explanation: The plot of PV VS P is not a straight line for real gases because they deviate from Ideal BEHAVIOUR. are there are two types of deviations one is a positive DEVIATION and the other is a negative deviation.

Right choice is (C) collisions of gas molecules are elastic

Easy explanation: Collisions are elastic as the TOTAL amount of energy before and after the collision is the same. The correct STATEMENTS of the incorrect ones are: in gases, there is a PREDOMINANCE of thermal energy, the distribution of SPEEDS remains constant at a particular temperature and the gases exert the same pressure in all directions of the container.

Right answer is (b) there are high forces of ATTRACTION between the gas molecules

The best explanation: According to Kinetic molecular THEORY of GASES, there are no forces of attraction between the particles of gas at normal temperature and pressure. This is because gases expand and occupy all the SPACE available.

The correct answer is (b) increases

To elaborate: From the kinetic MOLECULAR THEORY of gases we can know that the kinetic energy of an object is proportional directly to the Absolute Temperature of that object so when the temperature of an object increases OBVIOUSLY the kinetic energy ALSO increases.

Correct ANSWER is (a) perfectly elastic

Explanation: The total energy of molecules before the collision is equal to the total energy after the collision. That means there may be an EXCHANGE of energy between the molecules but the total energy does not CHANGE, so the COLLISIONS of gas molecules are elastic.

The correct OPTION is (b) different

Explanation: ACCORDING to the kinetic molecular THEORY of gases, the assumption that different particles have different speeds at a time is because particles do not ALWAYS have the same speeds and move in different directions but we can assume that the distribution of speeds is CONSTANT at a particular temperature.

Right ANSWER is (b) collide with each other during random motion

To explain I would say: As the particles of gas travel in STRAIGHT lines and move in a random motion and collide with each other and also collide with the WALLS of the CONTAINER, the pressure is exerted on the walls of the container in all DIRECTIONS.

The correct option is (a) true

The explanation: Particles do not have a fixed shape because they are ALWAYS in RANDOM motion and particles NEVER occupy fixed position the KEEP on moving and never occupy a particular shape this is the reason to prove that the above statement is true.

The correct option is (a) 11.533 m/s

For EXPLANATION: The formula for mean velocity of a GAS is given by the expression \(\SQRT{2RT/M}\). for one mole of neon gas M is TAKEN as 0.02 KG, temperature as 400 k, R as 8.314 kgm^2s^-2, so by substituting we get an answer as 11.533 m/s.

The correct choice is (b) \(\sqrt{10}\)

Best explanation: The formula of average speed is given by \(\sqrt{2RT/M}\). We KNOW that the velocity of gas molecules is inversely PROPORTIONAL to the root over the MASS of the gas. So here the RATIO of velocities is \(\sqrt{5×4/2×1}\) = \(\sqrt{10}\).

The correct answer is (b) HYDROGEN

For explanation: The formula of average SPEED is given by \(\sqrt{2RT/M}\), where R is universal gas constant, T is a TEMPERATURE in Kelvin and M is the MASS in kilograms. From the formula, we understand that the average speed is inversely proportional to the ROOT over the mass. As hydrogen has the least mass among the options it has the highest average speed.

Right answer is (B) 44.78 m/s

Explanation: The FORMULA for the most probable speed of a gas is given as \(\sqrt{8RT/πM}\). Here R is a universal gas constant which is ALWAYS EQUAL to 8.314 kgm^2s^-2, T=300 Kelvin and M = 0.032 kg So by substituting, we GET an answer as 44.78 m/s.

Right CHOICE is (b) false

Best explanation: The RATIO of root mean SQUARE speed to the mean probable speed is 1.224. So the above statement is CONSIDERED to be WRONG. The ratio between the main probable speed and the average speed and root mean square speed is 1: 1.128: 1.224.

The correct option is (c) root mean square speed

Explanation: According to the formula, the root mean square speed is greater than the AVERAGE speed and the average speed is greater than the most probable speed at GIVEN IDENTICAL CONDITIONS and for the same gas.

The correct ANSWER is (a) 2

The explanation: The formula of root MEAN square speed of particles is given as \(\sqrt{3RT/M}\). We know that the velocity of GAS molecules is inversely proportional to the root over the mass of the gas here the mass of oxygen to the mass of hydrogen RATIO is the answer. So \(\sqrt{16/4}\) = 2.

Correct answer is (a) 4.082 m/s

Best explanation: The root means SQUARE speed of particles is NOTHING but the square root over the SUM of squares of the particle’s speeds by a total NUMBER of particles. So by substituting, √3^2 + 4^2 + 5^2/3 = 4.082 m/s.

Right option is (c) 2735.43 m/s

The explanation: The formula of root mean square speed is given by URMS = \(\sqrt{3RT/M}\). We have R = 8.314 kgm^2/s^2, M = 10^-3 kg/mol and T = 300 k. So by SUBSTITUTING the formula we get, urms = \(\sqrt{3×8.314×300/10^{-3}}\) = 2735.43 m/s.

Right answer is (B) 1.224

Explanation: The ratio of root mean SQUARE speed, represented as urms to the most probable speed, represented as ump is always the same for IDENTICAL conditions and same GAS. It is \(\sqrt{3RT/M}\) DIVIDED by \(\sqrt{8RT/πM}\) = 1.224.

Right option is (a) 0.25

Explanation: The partial PRESSURE of a gas is given by the mole fraction of the gas X the TOTAL pressure, so the RATIO of the partial pressure to the total pressure is the mole fraction of nitrogen is 7/14 divided by 44/44 + 16/32 2 + 7/14 = 0.25.