In a double slit experiment, when one of the slits is covered by a transparent mica sheet of refractive index \(1.56,\) the central fringe shifts to the position of \(7^\text{th}\) bright fringe, obtained with both slits uncovered. If the light source wavelength is \(450~\text{nm},\) the thickness of mica sheet is \(\alpha \times 10^{-9} ~\text{m} .\) The value of \(\alpha\) is:
1. \(4500\)
2. \(5625\)
3. \(6300\)
4. \(7200\)
