Correct Answer: C. have variable oxidation states

Correct Answer: D) dissolution of potassium hydroxide pellets.

Explanation

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. In a chemical reaction, the bonds between atoms are broken and new bonds are formed, resulting in the production of new substances with different properties.

Option A: Burning of bush is a chemical reaction called combustion. During combustion, organic matter (like plants) reacts with oxygen in the air to produce carbon dioxide, water, and heat energy. So, this is a chemical reaction.

Option B: Rusting of iron is also a chemical reaction called oxidation. In this process, iron reacts with oxygen and water in the air to form hydrated iron(III) oxide, which is commonly known as rust. This is a chemical reaction as well.

Option C: Decay of bitter leaves involves the decomposition of organic matter by microorganisms. This process involves various chemical reactions that break down complex organic molecules into simpler substances such as carbon dioxide, water, and nutrients. Therefore, the decay of bitter leaves is a result of chemical reactions.

Option D: Dissolution of potassium hydroxide pellets is the correct answer because it is not a chemical reaction. Dissolution is a physical process where a solute (in this case, potassium hydroxide pellets) is dissolved in a solvent (usually water) to form a solution. In this process, no new substances are formed, and the bonds between the atoms in the solute are not broken or changed. Instead, the solute particles are simply surrounded by solvent molecules and dispersed evenly throughout the solution.

In summary, dissolution of potassium hydroxide pellets is not a chemical reaction, while burning of bush, rusting of iron, and decay of bitter leaves are all examples of chemical reactions.

Correct Answer: C. W and X only

Explanation

Among the given elements, W has the lowest ionization energy (\(12.0 KJ mol^{-1} x 10^{-3})\), indicating that it would be more likely to react with chlorine. X has a higher ionization energy \((21.0 KJ mol^{-1} x 10^{-3})\), so it would be less reactive with chlorine compared to W.

Based on ionization energy values, the elements that would react more readily with chlorine are W and X.

Correct Answer: B. Phenolphthalein

Explanation

Phenolphthalein is a common laboratory indicator used to detect the presence of bases in a solution. In its basic form (pH > 8.3), it turns pink or purple, indicating the presence of a base.

Correct Answer: A. cu²⁺

Explanation

The arrangement of elements in order of increasing electrode potential values is called electrochemical series.

K > Na > Ca > Mg > Al > Zn > Fe > Ni > Sn > Pb > H > Cu > Ag > Au.

Correct Answer: C) reforming

Explanation

(i) (1) Aeration/exposure to sunlight.

(2) Add alum/coagulation /flocculation.

(3) Sedimentation.

(4) Fi!teration.

(5) Add chlorine /disinfectant.

(6) Add flouride/iodide.

(7) Add Ca(OH)\(_2\) / pH control.

(ii) Cations that can cause hardness in water: Mg, Ca, Fe.

(iii)Disadvantages of Hardness of Water:

(1) It wastes soap.

(2) Forms stain on white clothing and material

(3) Forms boiler scale and kettle fur / damage.

(4) It is unsuitable for industrial processes, e.g. dyeing and tanning.

(iv) Sources of Water Pollution:

(1) Wastes from industries, e.g. brewery.

(2) Agricultural activities, e.g. fertilizer.

(3) Waste from quarry activities.

(4) Refuse from plant and animal origin.

(5) Sewage (industrial and domestic).

(6) Oil spillage.

(b)(i) Water is a polar solvent and can therefore easily dissolve sodium chloride which is ionic / polar salt. Oil, on the other hand, is non-polar and, hence cannot dissolve in water which is polar.

(ii) - H\(_2\)SO\(_4\) - As a dehydrating agent.

- H\(_2\)SO\(_2\) - As an acid.

- H\(_2\)SO\(_4\) As an oxidizing agent.

(c)(i) HCl and O\(_2\)

(ii)(I) Na\(_2\)CO\(_3\)

(II) Na\(_2\)CO\(_3\) is stable in air and can be weighed accurately. NaOH absorbs water / deliquescent and cannot be weighed accurately.

Correct Answer: B) 32

Correct Answer: D. Potassium dichromatic-sulphuric acid

Correct Answer: C. MO₃