An empty thick conducting shell of inner radius $a$ and outer radius $b$ is shown in figure.If it is observed that the inner face of the shell carries a uniform charge density $-\sigma$ and the surface carries a uniform charge density $ '\sigma '$

If a point charge $q_A$ is placed at the center of the shell, then choose the correct statement $(s)$

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  • A

    The charge must be positive

  • B

    The charge must be negative

  • C

    The magnitude of charge must be $4\ \pi \sigma a^2$

  • D

    $A$ and $C$ both

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  • [JEE MAIN 2022]

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