68th Prelims 2023

Explanation:

The image formed by the convex lens with thin strips of black paint on its surface will be a horse of less brightness. The black strips partially block some light, reducing overall brightness.

Explanation:

Shrillness or pitch of a sound depends on its frequency, which is inversely proportional to wavelength. Higher frequency = higher pitch.

Explanation:

Photovoltaic cells convert light to electrical energy and are widely used in digital devices like solar calculators.

Explanation:

Ball bearings reduce friction by converting static friction into rolling friction, enabling smoother movement.

Explanation:

Pulling hands backward extends the time over which momentum changes, decreasing the impact force on the hands.

Explanation:

Alpha rays are positively charged particles (2 protons + 2 neutrons). Beta rays are electrons or positrons; cathode rays are electrons.

Explanation:

Centripetal force acts towards the center of a circle, keeping objects in circular motion.

Explanation:

Friction converts kinetic energy into heat energy, as in moving tires or rubbing hands.

Explanation:

Passengers bend left due to inertia resisting the bus's sudden right turn.

Explanation:

Adjusting tension changes string frequency to match other instruments' frequencies for harmony.

Explanation:

All three are chemical changes, so 'More than one of the above' is correct.

Explanation:

Liquids have fixed volume but no fixed shape; kerosene is an example.

Explanation:

Nitrous oxide, methane, and carbon dioxide all trap heat and contribute to global warming.

Explanation:

Aluminium oxide (Al2O3) and zinc oxide (ZnO) react with both acids and bases.

Explanation:

Acid + metal carbonate → salt + water + CO2 gas.

Explanation:

HOOCCOOH is the chemical formula of oxalic acid.

Explanation:

Acetic acid gives vinegar its characteristic smell.

Explanation:

Bases turn red litmus paper blue; acids turn blue litmus red.

Explanation:

Dry HCl cannot produce H3O+ ions without water, so litmus color does not change.

Explanation:

Diamond and graphite differ in structure, hardness, and conductivity; so none of the individual statements is correct alone.

Explanation:

Stomata open when guard cells are turgid (full of water) and close when flaccid.

Explanation:

Chlorophyll absorbs red and blue light; green is reflected giving plants their green color.

Explanation:

Not all trees have thick hard stems with branching at base; the other matches are correct.

Explanation:

Transpiration pulls water upward through xylem by creating negative pressure.

Explanation:

Chloroplasts contain both DNA and RNA, allowing self-replication and protein synthesis.

Explanation:

Cartilage is flexible connective tissue allowing bending; bones like carpals and vertebrae are rigid.

Explanation:

Lichens are symbiotic associations between a fungus and a photosynthetic alga or cyanobacterium.

Explanation:

Female Anopheles mosquitoes rest at an angle; female Culex rest parallel to the surface.

Explanation:

Lymphocytes (B and T cells) are key to the immune response; platelets aid clotting, RBCs carry oxygen.

Explanation:

Muscles pull bones to move them; they cannot push. Other statements are correct.