Why bismuth has low m.p. while if going down the group m.p. increases?

This may presumably be due to more tendency of Bi to form three rather than five covalent bonds (inert pair effect). Thus there are weak forces of attraction between their atoms in solid state, accounting for its low m.p.

Related Questions:

Which is more basic N(CH3)3 or N(SiH3)3 , explain?

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Trisilyl amine, N(SiH3)3 is planar whereas trimethyl amines N(CH3)3 is pyramidal. Explain why?.

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Why Nitrogen is fairly inert gas?

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Why Nitrogen dioxide (NO2) dimerises to form Dinitrogen tetraoxide (N2O4)?

Why Nitrogen dioxide (NO2) is coloured but Dinitrogen tetraoxide (N2O4) is colourless?