Intense white light is incident on a diffraction grating that has $624$ lines$/$mm$.$

$($a$)$ What is the highest order in which the complete visible spectrum can be seen with this grating? $($Enter $1$ for first order, $2$ for second order, etc.$)$

$($b$)$ What is the angular separation between the violet edge $(400$ nm$)$ and the red edge $(700$ nm$)$ of the first order spectrum produced by the grating?

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