Part – B (General Studies) NDA/NA SOLVED PAPER 2018 (I) (51 to 100)

Total Questions: 50

31. A ball balanced on a vertical rod is an example of:

Correct Answer: (b) unstable equilibrium
Solution:

When the centre of gravity of a body lies below point of suspension or support, the body is said to be in stable equilibrium. When the centre of gravity of a body lies above the point of suspension or support, the body is said to be in unstable equilibrium.
A balanced ball on a vertical rod is an example of unstable equilibrium because when the rod is slightly disturbed its centre of gravity is lowered. The line of action of its weight lies outside the base of the rod.
Then the torque due to weight of the toppled it down. When the centre of gravity of a body lies at the point of suspension, the body is said to be inventral equilibrium.

32. Which of the following statements about a fluid at rest in a cup is/are correct?

1. Pressure is same-at all the points in the fluid.
2. Pressure is exerted on the walls.
3. Pressure exists everywhere in the fluid.
Select the correct answer 'using the codes given below

Correct Answer: (d) 1, 2 and 3
Solution:

When a fluid is at rest in a cup then pressure is same at all the points in the fluid, pressure is exerted on the walls and pressure exists everywhere in the fluid.
The pressure at a point within a volume of fluid means that the point to be surrounded by a small container by the area of the container.

33. Which one of the following devices is used to measure atmospheric pressure?

Correct Answer: (b) Barometer
Solution:

Barometer is used to measure the atmospheric pressure. The function of a barometer is to know whether or not atmospheric pressure is rising or falling. Ammeter is a device which is used to measure electric current in amperes. Potentiometer is used to measure the emf of a cell and. Loctometer is used to measure the purity of milk.

34. Which one of the following is the number of water molecules that share with two formula unit CaSO₄ in Plaster of Paris?

Correct Answer: (a) One
Solution:

35. How is carbon black obtained?

Correct Answer: (c) By burning hydrocarbons in a limited supply of air
Solution:Carbon black is obtained by burning hydrocarbons in a limited supply of air.It is used as a black pigment in black ink and as filler in automobile tyres. Which charcol and coke are obtained by heating wood or coal respectively at high temperature.

36. Which one of the following properties is NOT true for graphite?

Correct Answer: (a) Hybridisation of each carbon atom is sp³
Solution:

A graphite crystal consists of layers of carbon atoms or sheets of carbon atoms. Each carbon atom in a graphite layer is joined to other three carbon atoms by strong covalent bonds to form flat hexagonal rings.
In this case, only 3 of the 4 valence electrons of C participate in bonding. Thus, hybridisation is sp² having covalent bonds with other 3 C-atoms in same plane.
The electrons are delocalised over the whole sheet of atoms which makes it good conductor of electricity. Thus, among the given options, option ‘a’ is incorrect.

37. Which one of the following is the purest form of Carbon?

Correct Answer: (d) Carbon black
Solution:

Carbon black (lamp black) is the most purest form of carbon. It contains about 98-99% of carbon. It is used for making printer ink, black paint, varnishes and carbon papers.
Charcoal is the impure form of carbon because of its porous structure and large surface area.
Coke contains 80-85% carbon. It is used as a fuel and as a reducing agent in metallurgy.

38. The Poisonous nature of Carbon monoxide (CO) is due to its:

Correct Answer: (b) ability to form a complex with haemoglobin
Solution:

Carbon monoxide (CO) is highly poisonous to living beings because it has an ability to form more stable carboxyhaemoglobin. It is 300 times more stable than oxygenhaemoglobin complex.
In blood, when the concentration of carbonyhaemoglobin reaches about 3-4 per cent. The oxygen carrying capacity of blood is greatly reduced. The oxygen deficiency results into headache, weak eyesight, nervousness, etc.

39. Which one of the following elements is needed in the human body to transfer electrical signals by nerve cells?

Correct Answer: (b) Sodium
Solution:

Sodium in the form of ions are found in large proportions in biological fluids. It plays an important role in the transmission of nerve signals.
It also regulates the flow of water across cell membranes and in transport of sugars and amino acids into the cells.

40. Who among the following first discovered cell?

Correct Answer: (b) Robert Hooke
Solution:

Robert Hooke was the first who studied and discovered cell from a thin section of dead cork. He observed small honeycomb-like structures and named them as cells.
Robert Brown reported the discovery of nucleus. Leeuwenhock was the first person to observe living cells under microscope. Rudolf Virchow proposed that all cells arise from pre-existing cells.