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Calculation:

Work done by a force depends on the relative direction of force and displacement.

The relation for work done is W = F × d × cos(θ), where θ is the angle between force and displacement.

When the displacement is perpendicular to the direction of force, θ = 90°.

cos(90°) = 0

⇒ W = F × d × 0

⇒ W = 0

This shows that no work is done when force acts perpendicular to the displacement.

Therefore, the correct answer is Option 3.

Explanation:

The magnetic field inside a very long current-carrying solenoid is considered.

According to Ampere’s circuital law, the magnetic field inside a solenoid depends on the current and the number of turns per unit length.

The relation is B = μ₀ × n × I.

Here, μ₀ is the permeability of free space, n is the number of turns per unit length, and I is the current.

For a very long solenoid, end effects are negligible.

⇒ The magnetic field remains the same at all points inside the solenoid.

This shows that the magnetic field inside a very long solenoid is uniform.

Therefore, the correct answer is Option 1.

Explanation:

The temperature to be measured is −250°C, which lies in the extremely low temperature range.

Mercury thermometers are unsuitable because mercury freezes at about −39°C.

Clinical thermometers are limited to human body temperature ranges and cannot measure extreme cold.

Alcohol thermometers are also unsuitable since alcohol freezes near −114°C, which is much higher than −250°C.

Thermocouple-based thermometers are designed to measure very wide temperature ranges, including extremely low temperatures.

⇒ Only a thermocouple can reliably measure −250°C.

Therefore, the correct answer is Option 4.

Explanation:

The quantity of heat required to change the state of a substance without any change in temperature is considered.

When unit mass of a liquid changes into vapour at constant temperature, the heat supplied does not raise temperature but is used for phase change.

This heat is defined as specific latent heat.

Specific heat relates to temperature change, thermal capacity refers to total heat required for a body, and heat energy is a general term.

⇒ The given definition matches specific latent heat.

Therefore, the correct answer is Option 2.

Explanation:

The condition described refers to the temperature at which a liquid’s vapour pressure equals the surrounding atmospheric pressure.

At this stage, bubbles of vapour form throughout the liquid and rise to the surface.

This characteristic temperature is defined as the boiling point.

Melting point relates to solid–liquid change, while the other options do not describe vapour pressure equality.

⇒ The given definition corresponds to the boiling point.

Therefore, the correct answer is Option 2.

Explanation:

Surface tension depends on the cohesive forces between molecules at the surface of a liquid.

With an increase in temperature, molecular kinetic energy increases.

This weakens the cohesive forces acting at the surface.

⇒ Surface tension decreases as temperature increases.

It does not remain constant, nor does it increase with temperature.

The change is not symmetric for both increase and decrease in temperature.

Therefore, the correct answer is Option 2.

Explanation:

The sinking or floating of a body in water depends on the comparison of densities.

If the density of a body is greater than the density of water, the buoyant force is insufficient to support it.

Density condition for sinking is expressed as:

ρ_body > ρ_water

⇒ When the density of water is less than the density of the body, the body sinks.

If densities are equal, the body remains suspended, and if the body’s density is lower, it floats.

This directly matches the stated condition.

Therefore, the correct answer is Option 2.

Explanation:

When a fielder catches a fast-moving ball, the ball’s momentum must reduce to zero.

According to the impulse–momentum relation, impulse equals change in momentum.

Impulse = Force × Time

For a fixed change in momentum, increasing the time of contact reduces the force.

⇒ Lower force results in smaller acceleration of the ball.

By pulling the hands backward, the fielder increases contact time.

This reduces impact force and prevents injury while catching the ball safely.

Therefore, the correct answer is Option 1.

Explanation:

The apparent raising of the bottom of a water-filled tank is an optical effect.

When light travels from water to air, its speed changes.

This causes the light rays to bend at the boundary between the two media.

⇒ The bending of light leads to an apparent shift in the position of the tank bottom.

This phenomenon is known as refraction of light.

Hence, the bottom appears raised due to refraction.

Therefore, the correct answer is Option 2.

Explanation:

The term SONAR is an acronym related to the use of sound waves.

SONAR stands for Sound Navigation and Ranging.

It is used to detect, locate, and determine the distance of objects under water.

⇒ The name reflects its function of navigation and ranging using sound.

Other expansions do not match the accepted scientific meaning.

Therefore, the correct answer is Option 3.