Which fuel has the highest calorific value per gram?
A. Coal
B. Hydrogen
C. Wood
D. Methane
Answer: Option B
Solution (By JKSSB Mock Tests)
Hydrogen has the highest calorific value (~150 kJ/g or 141.9 MJ/kg) because it has no heavier atoms like carbon and its combustion produces water, a very stable product. Methane ~55.5 kJ/g, coal ~25-35 kJ/g, wood ~17 kJ/g. Hydrogen is a clean fuel, but storage and production challenges remain. It can be used in fuel cells or internal combustion engines.
Explanation:
Natural rubber (cis-1,4-polyisoprene) is an addition polymer of isoprene (2-methyl-1,3-butadiene). It is obtained from latex of rubber tree (Hevea brasiliensis). It is elastic but weak. Vulcanization with sulfur introduces cross-links, improving strength and elasticity. Ethene gives polyethylene; styrene gives polystyrene; vinyl chloride gives PVC.
Explanation:
In the sulfate ion (SO4 2-), the central sulfur atom is bonded to four oxygen atoms with no lone pairs on the sulfur. The steric number is 4 (4 sigma bonds + 0 lone pairs). A steric number of 4 corresponds to sp3 hybridization, resulting in a tetrahedral geometry.
Explanation:
Na₂CO₃ reacts with Ca²⁺/Mg²⁺ to form insoluble CaCO₃/MgCO₃, which are removed. This is permanent hardness removal. Boiling works for temporary hardness. Ion exchange is another method.
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