General Science Previous Year Questions (PYQ) with Answers – Page 90

Too little fluoride in drinking water leaves tooth enamel weak, so teeth decay more easily and develop cavities, called dental caries.

Flint glass contains lead oxide, which gives it a high refractive index and clarity, so it is used for lenses and prisms of optical instruments.

The SI unit of inductance is the henry, symbol H, named after the American scientist Joseph Henry. Inductance measures how strongly a coil opposes a change in the current through it by producing an induced emf.

Mature human red blood cells lose these organelles as they develop. Red blood cells are made in the red bone marrow and push out their nucleus and other organelles before entering the blood.

Plaster of Paris mixed with water sets within minutes into a hard mass, which is why doctors use it to make casts that hold broken bones in place.

Renin, released by the kidney, converts angiotensinogen made by the liver into angiotensin I, which is then changed into angiotensin II.

At a fixed speed v, centripetal acceleration equals v²/r, so a larger radius gives a smaller acceleration. An object moving in a circle at constant speed is still accelerating, because its direction keeps changing.

Dengue is known for lowering the platelet count, which can lead to bleeding in severe cases. Dengue is a viral disease spread by the bite of the Aedes mosquito, mainly Aedes aegypti, which breeds in clean, stagnant water and bites during the day.

This is false, because most antibiotics, starting with penicillin, come from microbes. Alexander Fleming discovered penicillin in 1928 from the mould Penicillium notatum, which stopped the growth of bacteria around it.

The molar mass of sodium-23 is 23 g, so 46 g is exactly 2 moles, and 2 moles contain twice the Avogadro number of atoms.

In this reaction water accepts a proton (H⁺) from the hydrogen sulphate ion and becomes the hydronium ion, H₃O⁺, and a proton acceptor is a base.

Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.

The American physicist Murray Gell-Mann proposed quarks in 1964 and gave them their name. Gell-Mann, and independently George Zweig, suggested that protons, neutrons and other such particles are built from smaller units.

Heavy water is D₂O: two atoms of deuterium joined to one atom of oxygen. Deuterium is the isotope of hydrogen with one proton and one neutron in its nucleus, so it is about twice as heavy as ordinary hydrogen.

Hydrogen bonds lock the molecules of ice into an open cage, so ice takes up more space than the same mass of liquid water.

The Food Safety and Standards Authority of India is the statutory body that lays down standards for food and regulates its manufacture, storage, sale and import across India.

Uric acid is the end product of the breakdown of purines, which come from the nucleic acids DNA and RNA, so gout patients are told to cut down purine-rich food.

Thomson proposed in 1904 that an atom is a sphere of positive charge with electrons embedded in it, like plums in a pudding or seeds in a watermelon.

On a frictionless surface the person can move only by throwing something out in one direction, and a sneeze pushes air forward so the body recoils backward.

All four terms come from physics and cosmology, the study of how the universe and its matter work. An event horizon is the boundary around a black hole beyond which nothing, not even light, can escape.