Chemistry MCQs

Notes:
Coal is often called the “buried sunshine” because it developed from the remains of plants and greens that existed as long as 400 million years ago.

• Most of coal was formed 300 million years ago, when much of Earth was covered in “steamy swamps.”
• As these greens died, they fell to the bottom of the floor, forming peat.
• The coalification process (transformation into coal) begins when the peat is physically and chemically altered.

Notes:
Silver bromide (AgBr), a soft, pale-yellow, water insoluble salt well known (along with other silver halides) for its unusual sensitivity to light. It being sensitive to light, when suspended in gelatin, its grains create a photographic emulsion. When exposed to light, silver bromide decomposes producing a photo graphic impression on photo graphic film.

Notes:
Ionic compounds have high meltin and boiling points. Also, ionic compounds can conduct electricity in their aqueous solution or in the molten state. Carbon compounds are chemical substances that contain carbon atoms bonded to any other element. Most carbon compounds are molecular and molecular compounds always have lower melting and boiling pointsthan ionic compounds. Carbon compounds are poor conductors of electricity as they form covalent bonds, so it does not give rise to free electrons.

Notes:
Nuclear fission is either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays), and releasing a very large amount of energy, even by the energetic standards of radioactive decay. Fission as encountered in the modern world is usually a deliberately produced man-made nuclear reaction induced by a neutron.

Notes:
Control rods are used in nuclear reactors to control the fission rate of uranium and plutonium. They are composed of chemical elements such as boron, silver, indium and cadmium that are capable of absorbing neutrons without themselves fissioning. Boron is used to absorb the extra neutrons produced to keep the reactor producing just as many neutrons as it consumes.

Notes:
The Sun is a huge, glowing sphere of hot gas. Most of this gas is hydrogen (about 70%) and helium (about 28%). Carbon, nitrogen and oxygen make up 1.5% and the other 0.5% is made up of small amounts of many other elements such as neon, iron, silicon, magnesium and sulphur.

Notes:
Carbon is one of the elements which shows allotropy. Allotropic of carbon can be either amorphous or crystalline. Three most famous ‘allotropes’ of pure carbon are diamond, graphite and Buckminster fullerene (C-60). In all three allotropes, the carbon atoms are joined by strong covalent bonds but in such different arrangements that the properties of the allotropes are very different.

Notes:
Muscle cramp is an involuntary sudden contraction of muscle. After a strenuous exercise muscles experience lack of oxygen. In the absence or insufficiency of oxygen, they respire anaerobically thereby producing lactic acid. The accumulation of lactic acid causes cramps in muscles.

Notes:
Paracelsus (1493-1541) showed that reactions in the human body involve chemical changes. He had employed chemicals for medicinal purposes. Cordus (1515-1544) made ether from sulphuric acid and alcohol. Helmont (1577-1644) discovered the carbon dioxide.

Notes:
Heavy water, formally called deuterium oxide (D2O), is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium, (also known as heavy hydrogen). In nuclear reactors, heavy water acts as a neutron moderator to slow down neutrons so that they are more likely to react with the fissile uranium-235 than with uranium-238.