251. The hair of shaving brush clings together when removed from water due to –

1. Surface tension
2. Viscosity
3. Elasticity
4. Friction

Option “1” is correct.
The forces inside the molecules of water also pulls in the hair on the shaving brush as they have less mass, and due to this surface tension in the surface of the water the hair sticks together.
252. How many units of electricity will be consumed if you use a 60-watt electric bulb for 5 hours everyday for 30 days?

1. 12
2. 9
3. 6
4. 3

Option “2” is correct.
We know that-
Number of unit = kilowatt hour = watt x hour /1000
=(60×30×5)/1000=9 unit.
253. The important nuclear fuel available in India in abundance is :

1. Uranium
2. Thorium
3. Iridium
4. Plutonium

Option “2” is correct.
According to a report of Department of Atomic Energy in India, there are approximately 10.70 million tons of monazite, which contains 9,63,000 tons of Thorium Oxide (ThO2). India is one country that has an abundance of thorium. Andhra Pradesh has 35% of thorium reserve of India.
254. On adding common salt to water, the boiling point and freezing point of water will:

1. Increase
2. Decrease
3. Decrease and increase respectively
4. Increase and decrease respectively

Option “4” is correct.
If salt is added to the water then the boiling point of water will increases. This happens as the boiling point is the temperature at which the vapor pressure of solvent becomes equal to the external atmospheric pressure. Similarly it also decreases the freezing point, which in turn will interfere with the frozen solution’s crystal structure. That means the temperature will have to be colder to overcome it and freeze the mixture anyway.
255. To keep drinks at the same temperature for quite sometime, the walls of thermos bottle are coated with:

1. Aluminium paint
2. Lead Powder
3. Silver layer
4. Mercury Layer

Option “3” is correct.
The glass or steel which is used in thermos bottle is coated with a silver layer to keep drinks at the same temperature for some time.
256. In microwave oven, the microwave tube used is-

1. A combination of klystron and magnetron tubes
2. Klystron tube
3. Magnetron tube
4. Travelling wave tube

Option “3” is correct.
The Magnetron tube is a high-powered vacuum tube which is used to produce high microwave energy.
257. Which of the following elements was first produced artificially?

1. Neptunium
2. Plutonium
3. Francium
4. Technetium

Option “4” is correct.
Technetium is a chemical element with atomic number 43. It was the first artificially produced element. Technetium was isolated by Carlo Perrier and Emilio segre in 1937.
258. The force exerted by a magnet is an example of _________.

1. Non-contact force
2. Muscular force
3. Contact force
4. Electrostatic force

Option “1” is correct.
The force exerted by a magnet is an example of Non-contact force.
259. During uniform motion of an object along a straight line, the ________ remains constant with time.

1. Time
2. Velocity
3. Acceleration
4. Distance

Option “2” is correct.
Uniform motion is defined as the motion of an object in which the object travels in a straight line and its velocity remains constant along that line as it covers equal distances in equal intervals of time, irrespective of the length of the time.
260. The impression of an image persists on the retina for about _________ of a second.

1. 1/10th
2. 1/8th
3. 1/16th
4. 1/5th

Option “3” is correct.
An image stays on the retina for about 1/16 of a second. This feature is called persistence of vision.

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