NDA 2016 Previous Year GK Questions with Answers

The correct answer is D, colloidal solution of two liquids. An emulsion is a colloid in which one liquid is spread as fine droplets through another liquid that does not mix with it. Milk is the common example, with droplets of fat spread through water, and butter is the reverse kind, with droplets of water held in fat. Soap and detergents work as emulsifying agents: they keep oil droplets suspended in water so that grease can be washed away. In an emulsion both the dispersed phase and the dispersing medium are liquids, and that is what the question is testing. A is wrong because it describes colloids in general and not an emulsion in particular. B is wrong because a true solution is homogeneous with particles of molecular size, while an emulsion is a colloid. C is wrong because distillation separates liquids by their boiling points and has nothing to do with colloids. Exam tip: an emulsion is liquid in liquid, while an aerosol is a liquid or solid in gas.

The correct answer is D, 2 gram of carbon. Three grams of hydrogen, 48 grams of oxygen and 42 grams of nitrogen each come to 1.5 moles, while two grams of carbon is only about 0.17 mole, so carbon holds a different number of particles. The number of moles is found by dividing the given mass by the molar mass, and equal moles always mean an equal number of particles. Hydrogen gas is H2 with a molar mass of 2, so 3 divided by 2 is 1.5 moles. Oxygen gas is O2 with a molar mass of 32, so 48 divided by 32 is 1.5 moles. Nitrogen gas is N2 with a molar mass of 28, so 42 divided by 28 is 1.5 moles. Carbon has an atomic mass of 12, so 2 divided by 12 is about 0.17 mole. A is wrong because 3 grams of hydrogen is 1.5 moles. B is wrong because 48 grams of oxygen is also 1.5 moles. C is wrong because 42 grams of nitrogen is 1.5 moles too. Exam tip: convert every mass to moles first.

The correct answer is B, Cytoplasm. Bacteria are prokaryotes, so their DNA lies free in the cytoplasm instead of being packed inside a nucleus. The single circular chromosome sits in a region of the cytoplasm called the nucleoid, which has no nuclear membrane around it. Many bacteria also carry small extra rings of DNA called plasmids, which often hold genes for antibiotic resistance and are the tools used to move genes in biotechnology. Option A is wrong because a true nucleus with a membrane is found only in eukaryotes such as plants, animals and fungi; bacteria have no such organelle. Option C is wrong because the cell membrane only controls what enters and leaves the cell, although the chromosome is loosely attached to it at one point. Option D is wrong because ribosomes, of the smaller 70S type in bacteria, build proteins from the instructions in the DNA and store no genetic material themselves. Exam tip: prokaryotes have a nucleoid and 70S ribosomes; eukaryotes have a true nucleus and 80S ribosomes.

The correct answer is A, Sodium bicarbonate (Sodium hydrogen carbonate). Baking soda is sodium hydrogen carbonate, NaHCO3, a mild base made by the Solvay process from brine, ammonia and carbon dioxide. On heating, or on meeting an acid such as the tartaric acid in baking powder, it gives off carbon dioxide, and it is these bubbles that make bread and cake rise. The same reaction makes it useful in soda acid fire extinguishers and as an antacid, since it neutralises excess hydrochloric acid in the stomach. Option B is wrong because sodium carbonate, Na2CO3, is washing soda, a much stronger base used for cleaning and in glass making. Option C is wrong because potassium bicarbonate is a different salt, used in some fire extinguishers and fertilisers, not in the kitchen. Option D is wrong because potassium carbonate is potash, used in soap and glass. Exam tip: baking soda NaHCO3, washing soda Na2CO3.10H2O, caustic soda NaOH, and bleaching powder Ca(OCl)Cl.

The correct answer is A, strength of the intermolecular forces of attraction. Melting means breaking the particles free of the forces holding them in a fixed lattice, so a higher melting point means stronger forces of attraction. Heat supplied at the melting point does not raise the temperature at all; it is used as latent heat of fusion to overcome those attractions. This is why ionic solids such as common salt melt near 800 degrees Celsius while wax, held together by weak forces, melts in the warmth of a hand. Option B is wrong because repulsive forces act only when particles are pushed very close and they do not hold a solid together. Option C is wrong because molecular mass is a poor guide, as heavy iodine melts far below lighter silica. Option D is wrong because size matters only through the strength of the forces it creates, not on its own. Exam tip: stronger intermolecular forces mean a higher melting point and a higher boiling point together.