Q51.
A hypothetical electromagnetic wave is show below.\\
\includegraphics[max width=\textwidth, alt={}, center]{f6006e98-4b99-4411-a1a7-86410189cba7-10_460_841_251_1030}
The frequency of the wave is $x \times 10 ^ { 19 } \mathrm {~Hz} . x =$ $\_\_\_\_$ (nearest integer)