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Question:

When metal 'M' is treated with NaOH, a white gelatinous precipitate 'X' is obtained, which is soluble in excess of NaOH. Compound 'X' when heated strongly gives an oxide which is used in chromatography as an adsorbent. Then metal 'M' is: Ca, Fe, Zn, Al

Fe

Zn

Al

Ca

Solution:

Al + NaOH → Al(OH)₃ (white ppt)
Al(OH)₃ + OH⁻ → [Al(OH)₄]⁻ (soluble)
Al(OH)₃ heat → Al₂O₃ + 3H₂O
Al₂O₃ used as adsorbent in column chromatography.
Therefore option C is correct