Mendeleev's periodic table faced several anomalies. Which of the following was one of them?
A. Isotopes were placed in different groups.
B. Cobalt and Nickel were placed in the wrong order of atomic mass.
C. Hydrogen was given a fixed position in Group 1.
D. Lanthanides and Actinides were placed in separate blocks.
Answer: Option B
Solution (By JKSSB Mock Tests)
Mendeleev placed Cobalt (atomic mass 58.9) before Nickel (atomic mass 58.7) to maintain chemical similarities, violating his own periodic law based on atomic mass. Isotopes weren't an issue then, and H's position was ambiguous, but the Co/Ni placement is a classic anomaly of his atomic mass-based table.
Explanation:
Zinc blende (ZnS) is first concentrated by froth flotation, then roasted in excess air to convert it to ZnO: 2ZnS + 3O₂ → 2ZnO + 2SO₂. ZnO is then reduced with coke at high temperature (smelting) or dissolved in H₂SO₄ and electrolyzed. Roasting is typical for sulfide ores to remove sulfur as SO₂.
Explanation:
Gamma rays are high-energy photons emitted from the nucleus when it transitions from excited state to lower energy state. Alpha/beta decay often leaves nucleus in excited state which emits gamma.
Explanation:
BOD stands for Biological Oxygen Demand. It is a measure of the amount of dissolved oxygen required by microorganisms to decompose the organic matter present in a water sample. High BOD indicates severe organic pollution and poor water quality for aquatic life.
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