For a reversible isothermal expansion of an ideal gas

A
$\begin{aligned} Δ S_{sys} = Δ S_{surr} = positive \end{aligned}$
B
$\begin{aligned} Δ S_{sys} = - Δ S_{surr} \end{aligned}$
C
$\begin{aligned} Δ S_{sys} = Δ S_{surr} = negative \end{aligned}$
D
$\begin{aligned} Δ S_{sys} = Δ S_{surr} = 0 \end{aligned}$

Solution:

In the reversible isothermal expansion, temperature of the system and surroundings are taken to be identical. Since heat absorbed by the system is equal to the heat lost by the surroundings, $Δ S_{sys}$ and $Δ S_{sum}$ will have equal value but carry opposite sign.

Solution:

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