${\sigma _1}$ and ${\sigma _2}$ are the electrical conductivities of $Ge $ and $Na$ respectively. If these substances are heated, then
ABoth ${\sigma _1}$ and ${\sigma _2}$ increase
B${\sigma _1}$ increases and ${\sigma _2}$ decreases
C${\sigma _1}$ decreases and ${\sigma _2}$ increases
DBoth ${\sigma _1}$ and ${\sigma _2}$ decrease
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B${\sigma _1}$ increases and ${\sigma _2}$ decreases
b (b) $Ge$ is semiconductor and $Na$ is a metal. The conductivity of semiconductor increases and that of the metals decreases with the rise in temperature.
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