Step 1: Understand the question.
A spectral line has wavelength $460\,\text{nm}$. We must find its frequency.
Step 2: Recall the wave relation.
For light, speed equals wavelength times frequency, $c = \lambda \nu$. So \[ \nu = \frac{c}{\lambda} \] with $c = 3 \times 10^8\ \text{m s}^{-1}$.
Step 3: Fix the units of wavelength.
Change nanometres into metres: $460\,\text{nm} = 460 \times 10^{-9}\,\text{m} = 4.6 \times 10^{-7}\,\text{m}$.
Step 4: Put the values in.
\[ \nu = \frac{3 \times 10^8}{4.6 \times 10^{-7}} \]
Step 5: Do the arithmetic.
Dividing $3$ by $4.6$ gives about $0.652$, and the powers of ten give $10^{8-(-7)} = 10^{15}$. So \[ \nu = 0.652 \times 10^{15} = 6.52 \times 10^{14}\ \text{Hz} \]
Step 6: Pick the answer.
Rounded, this is $6.5 \times 10^{14}\,\text{Hz}$, option (B).
\[ \boxed{\nu = 6.5 \times 10^{14}\ \text{Hz}} \]