CSS 2013 General Science and Ability MCQs

Question 21. Phosphorus is an essential component of one of the following biological molecules: (CSS 2013)

1. Amino acids

2. Nucleic acids  

3. Carbohydrates

4. None of these

Question 22. He was the first scientist to prove that planets move around the sun: (CSS 2013)

1. Archimedes

2. Galileo Galilei

3. John Kepler

4. None of these

Explanation — In 1515, a Polish priest named Nicolaus Copernicus proposed that the Earth was a planet like Venus or Saturn, and that all planets circled the Sun. When Galileo pointed his telescope into the night sky in 1610, he saw for the first time in human history that moons orbited Jupiter. Galileo also observed the phases of Venus, which proved that the planet orbits the Sun.

Question 23. Atom is made up of ______ different kinds of subatomic particles: (CSS 2013)

1. Three

2. Two

3. Four

4. Five

Question 24. Uranium is best used as nuclear fuel in one of the following forms: (CSS 2013)

1. U²³⁵  

2. U²³⁸

3. U²³⁷

4. None of these

Explanation — Uranium-238 is fissionable but not fissile. Fissionable means that an element undergoes fission after capturing a neutron of high or low energy, whereas fissile means that a nuclide which is fissionable can be induced to undergo fission with low energy thermal neutrons. Basically, it is not sustainable for a nuclear fission chain reaction because neutrons produced by the fission of uranium-238 have lower energies than the original neutrons. Capture of neutrons lead to the formation of Plutonium-239, this is known as fertile isotope. As you can see that uranium-238 contributes in the operation of nuclear reactions and hence is a good nuclear fuel. If you consider the rest radioactive elements, you can easily say that they do not meet the requirements for a good nuclear fuel.

Question 25. The Alpha particles are compact clusters of: (CSS 2013)

1. Electrons and Protons

2. Two Protons and Two Neutrons  

3. Three Protons and Three Neutrons

4. None of these

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