GATE 2026 CY – Question 43

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 choice

The structure of B4H10 is given below. Its styx number is

Tetraborane B4H10, with boron and hydrogen symbols.

4012
4102
2104
2014

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Correct answer: (A) 4012

Explanation

The **styx number** describes the bonding in a borane: s, t, y and x are the numbers of

s: three-centre B–H–B bridge bonds,
t: three-centre B–B–B bonds,
y: two-centre B–B bonds,
x: BH₂ groups (extra terminal H atoms).

For tetraborane(10), $\text{B}_4\text{H}_{10}$ (arachno):
- It has **four** B–H–B bridges: $s=4$.
- It has no three-centre B–B–B bonds: $t=0$.
- It has **one** ordinary B–B bond: $y=1$.
- It has **two** BH₂ groups: $x=2$.

The styx number is **4012** (option A). Check: $s+x=6$ extra H atoms beyond the four BH units, giving $4+6=10$ H atoms. ✓