Chemistry 2004 Jamb Examination

The correct option is B. -273°C.

According to Charles' law, the volume of a gas is directly proportional to its temperature (in Kelvin). When the temperature reaches absolute zero (-273°C), the volume of the gas theoretically becomes zero. This is based on the concept that at absolute zero, the gas molecules would have minimal kinetic energy, and thus, the volume would be zero.

The correct option is A. hydrogen and carbon(II) oxide.

When steam (water vapor) is passed over red-hot carbon (usually coke), a reaction known as the water-gas shift reaction occurs:

\[ \text{C} + \text{H}_2\text{O} \rightarrow \text{CO} + \text{H}_2\]

This reaction produces carbon monoxide (CO) and hydrogen gas (H₂).

The correct option is D. mordant.

Aluminum hydroxide is used in the dyeing industry as a mordant. A mordant is a substance that helps fix dyes onto fabrics by forming a coordination complex with the dye, enhancing the dye's adhesion and color stability on the material.

The correct option is B. electrons in the d orbitals.

Transition metals possess variable oxidation states because they have electrons in the d orbitals. The presence of these d-electrons allows for the loss of different numbers of electrons from both the s and d orbitals, leading to various oxidation states.

The correct option is D. charcoal.

Charcoal, specifically activated charcoal, is used in the decolorization of sugar. Its porous structure allows it to adsorb impurities and colorants from the sugar solution.

The correct option is A. the 2s and 2p atomic orbitals hybridize.

Carbon is tetravalent because its 2s and 2p atomic orbitals hybridize to form four equivalent sp³ hybrid orbitals. This hybridization allows carbon to form four covalent bonds with other atoms, making it tetravalent.

The correct option is D. reacts vigorous on exposure to air.

Sodium metal is always kept under oil because it reacts vigorously with water, producing sodium hydroxide and hydrogen gas. Keeping it under oil prevents it from coming into contact with moisture or air, which could lead to unwanted reactions.

The correct option is A. cooling a molten mixture of the metals.

Alloys are best prepared by melting the constituent metals together and then cooling the molten mixture. This process allows the metals to mix thoroughly and form a solid solution with desired properties.

The correct option is B. reduction.

Sulfur dioxide (SO₂) bleaches by acting as a reducing agent. It reduces the colored compounds to colorless forms, which is why it is used in bleaching and decolorizing applications.

The correct option is C. Chlorine.

Chlorine gas is denser than air and can be collected by the method of downward delivery. This method involves allowing the gas to flow downward into a container because it is heavier than air and will displace the air above it.