Which of the following molecules has a double covalent bond?
A. N₂
B. O₂
C. H₂
D. Cl₂
Answer: Option B
Solution (By JKSSB Mock Tests)
In an oxygen molecule (O₂), each oxygen atom has 6 valence electrons and needs 2 more to complete its octet. They share two pairs of electrons, forming a double covalent bond (O=O). H₂ and Cl₂ have single bonds, while N₂ has a triple covalent bond (N≡N).
Explanation:
Tropospheric ozone is not emitted directly; it forms by photochemical reactions of NOx and VOCs in sunlight. So it's a secondary pollutant. CO, SO₂, and lead are primary pollutants emitted directly from sources. Secondary pollutants include ozone, PAN (peroxyacetyl nitrate), and sulfuric acid mist. Ozone at ground level is harmful.
Explanation:
Teflon (PTFE) has a very low coefficient of friction and high heat resistance, making it ideal for non-stick coatings. Polystyrene is used in packaging, polyethylene in plastic bags, nylon in textiles and ropes. Teflon's monomer is tetrafluoroethene.
Explanation:
Mendeleev named the missing element eka-aluminium. When gallium was discovered (1875), its properties (density, oxide formula) closely matched Mendeleev's predictions, validating his table. Germanium was eka-silicon; scandium was eka-boron. These predictions were a triumph of the periodic law. Gallium has a low melting point (~30°C) and is used in semiconductors. Mendeleev corrected atomic masses based on group properties.
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