The wavelength of light absorbed by $P_r$ form of phytochrome is:

Phytochrome exists in two interconvertible forms. The $P_r$ (red-absorbing) form absorbs red light at a peak of approximately $660\text{nm}$ (the closest option provided is $660\text{nm}$, though $680\text{nm}$ is sometimes cited as the edge of the range). $P_{fr}$ (far-red-absorbing) absorbs far-red light at $730\text{nm}$. (Note: In standard texts, $P_r$ absorbs at $660\text{nm}$ and $P_{fr}$ at $730\text{nm}$).