The correct option is C sin−1(45)
cr−speed of light in rarer medium
cd−speed of light in denser medium.
As we know, the critical angle is,
sin C=1μ=1(crcd)
sin C=cdcr=2×1082.5×108=2025
sin C=45
C=sin−1(45)
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Hence, (C) is the correct answer.