Question

Which of these pairs were put by Mendeleev in the wrong order on the basis of increasing atomic mass in his table?
1..Oxygen and fluorine
2..Phosphorous and sulphur
3..Sodium and magnesium
4..Cobalt and nickel​

Answer 1

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→ Option 4

Cobalt and Nickel - Cobalt's weight is 58.93 while Nickel's is 58.69 but Coblat is placed before Nickel, making it a wrong order