c. Group 17

Explanation: The halogen elements belong to Group 17 of the long periodic table. They are characterized by having seven electrons in their outermost electron shell.

a. Sodium chloride

Explanation: Sodium chloride (NaCl) is an ionic compound, and its solid state is composed of a regular arrangement of ions (sodium ions and chloride ions) held together by ionic bonds.

c. Liquid HCl

Explanation: Liquid HCl (hydrochloric acid) has the highest ability to conduct electricity among the options given. This is because it is a strong acid that dissociates completely into ions in its liquid state, providing a high concentration of ions that can conduct electricity.

NO

Explanation: During lightning, the high energy breaks the nitrogen (N₂) and oxygen (O₂) molecules in the atmosphere, leading to the formation of nitrogen monoxide (NO). This is a key step in the nitrogen fixation process that converts atmospheric nitrogen into compounds that can be used by living organisms.

c. Al₂O₃.2H₂O

Explanation: Bauxite, the primary ore of aluminium, is commonly represented by the formula Al₂O₃·2H₂O, indicating it is an aluminium oxide hydrate. The specific form of bauxite can vary, but it generally contains aluminium oxide combined with water.

b. Ethyl

Explanation: The ethyl group is the alkyl group containing two carbon atoms. Its formula is C₂H₅.

• Methyl is a one-carbon alkyl group (CH₃).
• Propyl has three carbon atoms (C₃H₇).
• Isopropyl is a branching form of propyl, also containing three carbon atoms.

The unit of calorific value of fuel is Joules per kilogram (J/kg) or kilocalories per kilogram (kcal/kg).

OR

In the stratosphere, the temperature increases with an increase in altitude.

The ozone layer prevents ultraviolet (UV) radiation from reaching the Earth's surface.

False.

Number of moles = 224\over 22.4 = 10 mole

Mass = Number of moles × Molar mass

= 10 × 28

= 280 grams

False

Explanation: During the conduction of heat through a material, the constituent particles (atoms or molecules) do not change their position. Instead, heat is transferred through the vibration or movement of these particles within their fixed positions.

OR

The relation between thermal resistance (R_th ​) and thermal conductivity (k) of a conductor is given by:

R_th = L/kA

When a ray of light passes through the center of curvature of a concave mirror, the angle of incidence is 0 degrees.