In the given figure switches $S_{1}$ and $S_{2}$ are in open condition. The resistance across $a b$ when the switches $S_{1}$ and $S_{2}$ are closed is $...\,\Omega$
A$5$
B$63$
C$10$
D$4$
JEE MAIN 2021, Diffcult
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C$10$
c $\frac{12 \times 6}{12+6}+2+\frac{6 \times 12}{6+12}$
$\frac{72}{18}+2+\frac{72}{18}=4+2+4=10\, \Omega$
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