Chemistry [ 2 Marks Questions ]

1. Silicones are used for low temperature lubrication and in vacuum pumps, high-temperature oil baths, etc.
2. They are used for making water proofing clothes.
3. They are used as insulting material in electrical motors and other appliances
4. They are mixed with paints and enamels to make them resistant towards high temperature, sunlight, dampness and chemicals.

1. The valency of an element is greater than or equal to two.
2. Element should have the ability to bond with itself.
3. The self-bond must be as strong as its bond with other elements.
4. Kinetic inertness of catenated compounds towards other molecules.
5. Carbon possesses all the above properties and forms a wide range of compounds with itself.

• Borax is used for the identification of coloured metal ions.
• In the manufacture optical and borosilicate glass, enamels and glazes for pottery.
• It is also used as a flux in metallurgy and also acts as a good preservative.

The following factors are responsible for this anomalous behaviour.

1. Small size of the first member.
2. High ionisation enthalpy and high electronegativity.
3. Absence of d-orbitals in their valance shell.

The first member of group-13, boron is a metalloid while others are reactive metals. Moreover, boron shows a diagonal relationship with silicon of group -14. The oxides of boron and silicon are similar in their acidic nature.

1. Silicon tetrachloride is used in the production of semiconducting silicon.
2. It is used as a starting material in the synthesis of silica gel, silicic esters, a binder for ceramic materials.

1. Rhombus
2. Monoclinic

1. White phosphorous
2. Red phosphorous (v)
3. Scarlet phosphorous
4. Violet phosphorous
5. Black phosphorous

1. Grey tin
2. White tin
3. Rhombic tin
4. Sigma tin

1. Amorphous boron
2. a-rhombohedral boron
3. p-rhombohedral boron
4. γ – rhombohedral boron
5. α – tetragonal boron
6. β – tetragonal boron