$K_b$ for $NH_4OH$ is $1.8\times 10^{-5}.$ The $[\mathop O\limits^\Theta  H]$ of $0.1\,M\,NH_4OH$ is

  • A

    $5.0\times 10^{-2}$

  • B

    $4.20\times 10^{-3}$

  • C

    $1.34\times 10^{-3}$

  • D

    $1.8\times 10^{-6}$

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