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GATE 2022 CY – Question 53

Inorganic Chemistry · Main Group Elements: Shapes and structures of molecules using VSEPR postulates, Hydrides, halides, oxides, oxoacids, nitrides, sulfides - shapes and reactivity. Structure and bonding of boranes, carboranes, silicones, silicates, boron nitride, borazine and phosphazenes: electron counting in polyhedral boranes, isolobal analogy. Allotropes of carbon, phosphorus and sulfur. Industrial synthesis of compounds of main group elements such as NH3, H2SO4 and HNO3. Chemistry of noble gases and interhalogen compounds. Acid-base concepts and principles (Lewis, Brønsted, HSAB and acid-base catalysis). · 2 marks · Multiple select

Which statements about $B_{10}H_{14}$ are correct?

  1. Brønsted acidity of $B_{10}H_{14}$ exceeds that of $B_5H_9$
  2. $B_{10}H_{14}$ is structurally a closo-borane
  3. Metal-promoted fusion of $B_5H_8^-$ produces $B_{10}H_{14}$
  4. $B_{10}H_{14}$ and $B_{10}H_{12}(SEt_2)_2$ have the same number of valence electrons

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Correct answer: (A) Brønsted acidity of $B_{10}H_{14}$ exceeds that of $B_5H_9$; (C) Metal-promoted fusion of $B_5H_8^-$ produces $B_{10}H_{14}$; (D) $B_{10}H_{14}$ and $B_{10}H_{12}(SEt_2)_2$ have the same number of valence electrons; (A) Brønsted acidity of $B_{10}H_{14}$ exceeds that of $B_5H_9$; (C) Metal-promoted fusion of $B_5H_8^-$ produces $B_{10}H_{14}$

Explanation

Decaborane is more acidic thanpentaborane, A true, and is nido rather thancloso, B false. Metal-promoted fusion of B5H8− can form the B10 framework, C true. Ordinary valence counting givesB10H14:44 electrons and B10H12L2 with two neutral donors:46, so D is not required. The finalkey accepts **A, C** as well as **A, C, D**; both combinations are stored.