Defence 2016 Previous Year GK Questions with Answers

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.