The critical angle for a denser-rarer interface is \( 45^\circ \). The speed of light in rarer medium is \( 3 \times 10^8 \, \text{m/s} \). The speed of light in the denser medium is:
\( \sqrt{2} \times 10^8 \, \text{m/s} \)
\( 5 \times 10^7 \, \text{m/s} \)
\( 2.12 \times 10^8 \, \text{m/s} \)
\( 3.12 \times 10^7 \, \text{m/s} \)