JEE Main · 2021 · Shift-IeasyPERI-072

The set in which compounds have different nature is:

Classification of Elements & Periodicity · Class 11 · JEE Main Previous Year Question

Question

The set in which compounds have different nature is:

Options
  1. a

    \ceB(OH)3\ce{B(OH)_3} and \ceH3PO3\ce{H3PO3}

  2. b

    \ceB(OH)3\ce{B(OH)_3} and \ceAl(OH)3\ce{Al(OH)_3}

  3. c

    \ceNaOH\ce{NaOH} and \ceCa(OH)2\ce{Ca(OH)_2}

  4. d

    \ceBe(OH)2\ce{Be(OH)_2} and \ceAl(OH)3\ce{Al(OH)_3}

Correct Answerb

\ceB(OH)3\ce{B(OH)_3} and \ceAl(OH)3\ce{Al(OH)_3}

Detailed Solution

🧠 The question wants the pair that DIFFERS in nature — find one acidic + one basic, or one amphoteric + one not Each option lists two compounds. You need to know each compound's nature, then spot the pair that is mismatched.

🗺️ Classify each compound \ceB(OH)3\ce{B(OH)3}: boric acid — Lewis acid, acidic. \ceH3PO3\ce{H3PO3}: phosphorous acid (diprotic) — acidic. \ceAl(OH)3\ce{Al(OH)3}: classic amphoteric hydroxide. \ceNaOH\ce{NaOH}: strong base. \ceCa(OH)2\ce{Ca(OH)2}: strong base. \ceBe(OH)2\ce{Be(OH)2}: amphoteric (Be is at the diagonal boundary).

Now scan the options: (a) \ceB(OH)3\ce{B(OH)3} acidic + \ceH3PO3\ce{H3PO3} acidic → same nature. (b) \ceB(OH)3\ce{B(OH)3} acidic + \ceAl(OH)3\ce{Al(OH)3} amphoteric → different nature. ✓ (c) \ceNaOH\ce{NaOH} basic + \ceCa(OH)2\ce{Ca(OH)2} basic → same. (d) \ceBe(OH)2\ce{Be(OH)2} amphoteric + \ceAl(OH)3\ce{Al(OH)3} amphoteric → same.

⚠️ The trap Many students mark (d) thinking Be(OH)₂ is "just another Group 2 hydroxide" and so basic. But Be is the exception in Group 2 — its hydroxide is amphoteric, just like Al(OH)₃. Both behave the same way. The real "different pair" is (b).

Answer: (b)\boxed{\text{Answer: (b)}}

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