I think it is either D) or E)
But i am going to go with E)
Answer:
0.82 mm
Explanation:
The formula for calculation an
bright fringe from the central maxima is given as:

so for the distance of the second-order fringe when wavelength
= 745-nm can be calculated as:

where;
n = 2
= 745-nm
D = 1.0 m
d = 0.54 mm
substituting the parameters in the above equation; we have:

= 0.00276 m
= 2.76 × 10 ⁻³ m
The distance of the second order fringe when the wavelength
= 660-nm is as follows:

= 1.94 × 10 ⁻³ m
So, the distance apart the two fringe can now be calculated as:

= 2.76 × 10 ⁻³ m - 1.94 × 10 ⁻³ m
= 10 ⁻³ (2.76 - 1.94)
= 10 ⁻³ (0.82)
= 0.82 × 10 ⁻³ m
= 0.82 × 10 ⁻³ m 
= 0.82 mm
Thus, the distance apart the second-order fringes for these two wavelengths = 0.82 mm
Sodium (Na) is a Alkali metal so that's the answer
I think that the answer is A