130. Which fertiliser among these primarily supplies nitrogen?
[UPSC NDA — 2024]
(A) Superphosphate
(B) Potassium sulphate
(C) Bone meal
(D) Urea
Answer: (D) Urea
Explanation: Urea is nitrogen-rich, containing approximately 46% nitrogen by mass. Superphosphate primarily supplies phosphorus, whereas potassium sulphate supplies potassium. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
129. Which combination catalyses hydrogen addition to an unsaturated hydrocarbon?
[UPSC CDS — 2024]
(A) Copper and hydrogen
(B) Iron and hydrogen
(C) Zinc and hydrogen
(D) Nickel and hydrogen
Answer: (D) Nickel and hydrogen
Explanation: Nickel acts as a catalyst during hydrogenation of unsaturated carbon-carbon bonds. This reaction adds hydrogen across the double or triple bond and produces a more saturated substance. Hydrogen participates in many compounds whose reactivity differs markedly with the bonded elements.
128. Which statement is correct about chlorine and fluorine?
[SSC MTS — 2024]
(A) Chlorine has highest electron affinity; fluorine highest electronegativity
(B) Fluorine has highest electron affinity; chlorine highest electronegativity
(C) Fluorine has both highest electron affinity and electronegativity
(D) Fluorine has highest electron affinity; bromine highest electronegativity
Answer: (A) Chlorine has highest electron affinity; fluorine highest electronegativity
Explanation: Fluorine attracts shared bonding electrons most strongly and is the most electronegative element. Chlorine releases slightly more energy on gaining an electron, owing partly to reduced crowding in its larger outer orbital. The chemical properties of group-17 elements follow from their seven outer-shell electrons.
127.
126. Which noble gas produces a characteristic red-orange glow when electricity passes through it?
[SSC CGL — 2024]
(A) Neon
(B) Hydrogen
(C) Argon
(D) Helium
Answer: (A) Neon
Explanation: An electric discharge excites neon atoms, whose returning electrons emit strong red-orange spectral lines. Neon is a noble gas and is used in illuminated signs because of its distinctive colour. These group-18 gases usually exist as single atoms rather than bonded diatomic molecules.
125. Which of the following is NOT considered an important greenhouse gas?
[SSC CGL — 2024]
(A) Methane
(B) Carbon dioxide
(C) Nitrous oxide
(D) Nitric oxide
Answer: (D) Nitric oxide
Explanation: Carbon dioxide, methane and nitrous oxide absorb infrared radiation and contribute significantly to greenhouse warming. Nitric oxide is a reactive atmospheric gas, but it is not classified as a major greenhouse gas. Atmospheric gases differ in how strongly they absorb infrared wavelengths emitted by Earth.
124. Which chemical symbol represents an element that is NOT a halogen?
[SSC CGL — 2024]
(A) F
(B) He
(C) Cl
(D) Br
Answer: (B) He
Explanation: Helium belongs to group 18, the noble gases. Fluorine, chlorine and bromine belong to group 17, the halogens. Halogens are generally reactive, whereas helium is exceptionally unreactive. These group-18 gases usually exist as single atoms rather than bonded diatomic molecules.
123. What are the elements of group 17 in the periodic table called?
[SSC MTS — 2024]
(A) Noble gases
(B) Alkali metals
(C) Halogens
(D) Transition metals
Answer: (C) Halogens
Explanation: The group-17 elements are halogens, including fluorine, chlorine, bromine and iodine. They commonly gain one electron to form halide ions and react with metals to form salts. The chemical properties of group-17 elements follow from their seven outer-shell electrons.
122. When diluting concentrated nitric acid, which is correct?
1. Hydronium concentration increases.
2. Water is slowly added to acid.
3. Acid is slowly added to water.
[UPSC CDS — 2023]
(A) 1, 2 and 3
(B) 1 and 2 only
(C) 3 only
(D) 2 and 3 only
Answer: (C) 3 only
Explanation: Acid must be added slowly to water with stirring because dilution is strongly exothermic. Adding water to concentrated acid may cause violent splashing; dilution reduces hydronium concentration. The concentration and mobility of ions help explain the observed chemical behaviour in solution.
121. Arrange these substances in increasing pH.
[UPSC CDS — 2023]
(A) Coffee < Lemon juice < Milk of magnesia < Blood
(B) Milk of magnesia < Blood < Coffee < Lemon juice
(C) Lemon juice < Blood < Coffee < Milk of magnesia
(D) Lemon juice < Coffee < Blood < Milk of magnesia
Answer: (D) Lemon juice < Coffee < Blood < Milk of magnesia
Explanation: Lemon juice is strongly acidic, coffee is mildly acidic, blood is slightly alkaline and milk of magnesia is more alkaline. Increasing pH follows that order. In aqueous chemistry, acidity depends on dissolved ionic species and the prevailing conditions.
