Wider grating spacing lowers the sine marker for the same order and wavelength. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Small spacing reaches the endpoint marker
Spacing 4 m times sine marker 1 gives 4 m. Order 2 times wavelength 2 m gives 4 m, so this row is accepted.
4m⋅1=4mmλ=2⋅2m=4mA=1
Wider spacing lowers the sine marker
Spacing 5 m times sine marker 4/5 gives 4 m. Order 2 times wavelength 2 m gives 4 m, so this row is accepted.
5m⋅54=4mmλ=2⋅2m=4mA=1
Double spacing halves the marker again
Spacing 10 m times sine marker 2/5 gives 4 m. Order 2 times wavelength 2 m gives 4 m, so this row is accepted.