In Young's double slit experiment, the wavelengths of red and blue lights used are $7.5 \times 10^{-5} \mathrm{~cm}$ and $5 \times 10^{-5} \mathrm{~cm}$ respectively. If $\mathrm{n}^{\text {th }}$ bright fringe of red color coincides with $(n+1)^{\text {th }}$ bright fringe of blue colour, then the value of ' $n$ ' is

• A

  $1$
• Correct answer
  B

  $2$
• C

  $4$
• D

  $8$

Hence, the correct answer is option: 'B'.