150. Which statements about phosphorus oxyacids are true?
I. H3PO4 is tribasic.
II. All three hydrogens in H3PO3 are ionisable.
III. Orthophosphate salts are used in fertilisers.
[UPPSC LT Grade (Science) — 2025]
(A) I and II
(B) II and III
(C) I and III
(D) I, II and III
Answer: (C) I and III
Explanation: H3PO4 has three hydroxyl groups and is tribasic. H3PO3 has only two ionisable hydroxyl hydrogens because its third is bonded directly to phosphorus. Phosphate salts are important fertiliser ingredients. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
149. Which reaction demonstrates acidic behaviour of ethanoic acid?
[RRB Group D — 2025]
(A) Ethanoic acid + ethanol → ester + water
(B) Ethanoic acid + sodium → sodium ethanoate + hydrogen
(C) Ethanoic acid + sodium hydroxide → sodium ethanoate + water
(D) Ethanoic acid + methanol → methanoic acid + ethane
Answer: (C) Ethanoic acid + sodium hydroxide → sodium ethanoate + water
Explanation: The selected acid-base neutralisation forms sodium ethanoate and water from ethanoic acid and sodium hydroxide. Neutralisation exemplifies reaction of an acid with a base. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
148. Which gas is released when baking soda reacts with vinegar?
[RRB NTPC — 2025]
(A) Carbon dioxide
(B) Carbon monoxide
(C) Ammonia
(D) Hydrogen
Answer: (A) Carbon dioxide
Explanation: Sodium hydrogen carbonate reacts with acetic acid in vinegar to form sodium acetate, water and carbon dioxide. The escaping carbon dioxide produces visible fizzing. Water solubility and hydration are often as important as composition in their practical use.
147. Carbonylation of methanol is an industrial preparation route for which acid?
[RRB NTPC — 2025]
(A) Nitric acid
(B) Citric acid
(C) Acetic acid
(D) Hydrochloric acid
Answer: (C) Acetic acid
Explanation: Methanol reacts with carbon monoxide under catalytic conditions to form acetic acid. This carbonylation route is a major industrial production method for ethanoic acid. Carbon forms stable covalent bonds, including single and multiple bonds, across many molecular structures.
146. Which industrial chemical is manufactured using the Contact Process?
[RRB NTPC — 2025]
(A) Ammonia
(B) Nitric acid
(C) Hydrochloric acid
(D) Sulphuric acid
Answer: (D) Sulphuric acid
Explanation: In the Contact Process, sulphur dioxide is catalytically oxidised to sulphur trioxide, commonly with vanadium(V) oxide. Further processing produces concentrated sulphuric acid, an important industrial reagent. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
145. Acid rain is chiefly caused by which two atmospheric gases?
[RRB NTPC — 2025]
(A) Oxygen and hydrogen
(B) Carbon dioxide and carbon monoxide
(C) Nitrogen and methane
(D) Sulphur dioxide and nitrogen oxides
Answer: (D) Sulphur dioxide and nitrogen oxides
Explanation: Sulphur dioxide and nitrogen oxides react with atmospheric oxidants and moisture to form sulphuric and nitric acids. Their acid deposition harms soil, lakes, vegetation and exposed buildings. Rainwater acidity is monitored because deposition changes both soil chemistry and lake water quality.
144. Which of these gases is monatomic under normal conditions?
[SSC CGL (2024 cycle, Tier II) — 2025]
(A) Chlorine
(B) Hydrogen
(C) Xenon
(D) Oxygen
Answer: (C) Xenon
Explanation: Xenon is a group-18 noble gas existing as individual atoms in ordinary gas conditions. Chlorine, hydrogen and oxygen occur as diatomic molecules, so xenon is the only monatomic choice. These group-18 gases usually exist as single atoms rather than bonded diatomic molecules.
143. Which is an amphoteric oxide?
[UPSC CDS — 2024]
(A) MgO
(B) P4O10
(C) Na2O
(D) Al2O3
Answer: (D) Al2O3
Explanation: Aluminium oxide reacts with both strong acids and alkalis, demonstrating amphoterism. Magnesium oxide and sodium oxide are basic, while phosphorus oxide is acidic. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
142. Vinegar is most accurately described as what?
[UPSC CDS — 2024]
(A) About 5–8% acetic acid in water
(B) About 5–8% carbonic acid in water
(C) About 5–8% ethanol in water
(D) About 10–15% propionic acid in water
Answer: (A) About 5–8% acetic acid in water
Explanation: Ordinary vinegar is a dilute aqueous solution of acetic acid, often roughly five to eight percent. Its acidity gives vinegar its characteristic sour taste. Organic acids share acidic behaviour but differ in molecular structure, biological origins and uses.
141. Match bleaching powder, baking soda, washing soda and plaster of Paris to their chemical names.
[UPSC CDS — 2024]
(A) Calcium oxychloride, sodium bicarbonate, sodium carbonate decahydrate, calcium sulphate hemihydrate
(B) Calcium oxychloride, sodium carbonate, sodium bicarbonate, calcium sulphate hemihydrate
(C) Calcium sulphate, sodium carbonate, sodium bicarbonate, calcium oxychloride
(D) Calcium sulphate, sodium bicarbonate, sodium carbonate, calcium oxychloride
Answer: (A) Calcium oxychloride, sodium bicarbonate, sodium carbonate decahydrate, calcium sulphate hemihydrate
Explanation: The named salts have established compositions: bleaching powder is conventionally CaOCl2, baking soda NaHCO3, washing soda Na2CO3·10H2O, and plaster of Paris CaSO4·½H2O. Water solubility and hydration are often as important as composition in their practical use.
