General Science MCQ Practice

Correct answer: C

• The pH scale ranges 0–14. A value >7 indicates alkaline (basic) soil;

• Reason: Olive Ridley refers to a sea turtle species (Lepidochelys olivacea). It is famous for arribadas (mass nesting) in warm tropical oceans.
• Key concept: Common animal names in biology; Olive Ridley is not related to conflicts or birds.
• Other options: B, C, D are incorrect because they describe human or bird topics, not this turtle species.
• Exam tip: Questions often ask for species names; memorize a few common ones like Olive Ridley = sea turtle.

• Why correct: Dolomite is calcium magnesium carbonate (CaMg(CO3)2). It is used as a soil conditioner/liming agent to raise soil pH and supply Ca and Mg for better soil structure and fertility.
• Key concept: Liming to neutralize soil acidity and improve nutrient availability.
• Other options: Not used for pasteurization, dynamite, or synthetic rubber.
• Exam tip: Remember “Dolomite = CaMg(CO3)2” and its agricultural use as lime.

• Vinegar is a solution of diluted acetic acid (CH3COOH) in water along with trace compounds that give its smell and taste.
• Key concept: acid in solution; acetic acid is a weak acid, giving acidic pH in dilute form.
• Why others are incorrect: A) citric acid is in citrus fruits, not vinegar; C) hydrochloric acid is strong and not used in vinegar; D) oxalic acid is a different acid not typical in vinegar.
• Exam tip: remember “vinegar = acetic acid” due to its distinctive sour taste and usage in pickling.

• Reason: ISRO (Indian Space Research Organisation) was established in 1969.
• Key concept: National space agencies form to advance space research and applications.
• Why option C is correct: It exactly matches the official founding year.
• Why others are incorrect: A (1976) and D (1970) are incorrect founding years; B (1966) refers to the initial space program ideas, not ISRO’s establishment.

• Why correct: Joseph Priestley discovered oxygen in 1774 by heating mercuric oxide and later naming it “dephlogisticated air.” This identified oxygen as a distinct gas.
• Key concept: Oxygen is a gas required for combustion and respiration; it is produced by various chemical reactions and is a basic element in air (O2).
• Tip: Remember “Priestley, Priest-ley” for the discovery link to oxygen and experiments with gases.
• Why others are incorrect: Rutherford (nuclear physics), Harvey (circulation theory), Galileo (astronomy/physics) did not discover oxygen.

• The atmosphere is mostly nitrogen (≈78%), followed by oxygen (≈21%).
• Key concept: Ideal gas composition of dry air; nitrogen is chemically inert, making it the most abundant gas near Earth’s surface.
• If formula is needed: not required here, but approximate fractions are N2 ≈ 78%, O2 ≈ 21%.
• Exam tip: Remember the major components by percentage; nitrogen is the dominant gas.
• Why others are incorrect: Oxygen is abundant but not the most; hydrogen and methane are trace gases in the atmosphere.

• The correct answer is B. Virtual and erect.
• A concave (diverging) lens causes rays to spread apart. When objects are placed anywhere, the extensions of the refracted rays appear to come from a point on the same side as the object, producing a virtual image that is erect.
• Key concept: diverging lens forms virtual, upright images; image is usually diminished in size.
• Formula note: for a concave lens, the image distance is negative in sign convention, indicating a virtual image.
• Exam tip: If not asked about magnification, remember concave lenses cannot form real images for real objects placed at standard positions.
• Why other options are wrong: A and C claim real images; D claims inverted, which occurs with many converging systems, not with a single concave lens.