DEAR JAUNEET,
It is stable only at low temperatures. When heated at temperature between 373 K and 575 K, it changes into higher boranes. The elements of group 13 have three electrons in their valence shell (ns2npl)  and, therefore, exhibit, oxidation state of + 3. However, it bas been  observed that in addition to + 3 oxidation state, they also exhibit  oxidation state of +1. The +1 oxidation state becomes more and more  stable as one goes down the group from B, Al, Ga, In to Tl. The +1  oxidation state of Tl is more stable than +3 oxidation state. For e.g.,  thallous compounds such as TlOH and TlClO4 are more stable  than their thallic compounds. This is attributed to the inert pair  effect. In the case of last element, after the removal of one electron  from p-orbital, the remaining ns2 (e.g. 6s2)  electrons behave like stable noble gas and do not take part formation.  This reluctance of the s-electron pair to take part in chemical  combination is called inert pair effect. This helps to explain the  stability of borane.



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Sagar Singh
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