Light Having a Frequency in Vacuum Of $6.0 \times 10 ^ { 14 } \mathrm {~Hz}$

Light having a frequency in vacuum of $6.0 \times 10 ^ { 14 } \mathrm {~Hz}$ enters a liquid of refractive index $2.0$ . What is the frequency of the light in this liquid? $\left( c = 3.0 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } \right)$

A) $6.0 \times 10 ^ { 14 } \mathrm {~Hz}$
B) $3.0 \times 10 ^ { 14 } \mathrm {~Hz}$
C) $2.0 \times 10 ^ { 14 } \mathrm {~Hz}$
D) $1.5 \times 10 ^ { 14 } \mathrm {~Hz}$
E) $12 \times 10 ^ { 14 } \mathrm {~Hz}$