This question has a paragraph followed by two statements,Statement $- 1$ and Statement $- 2$. Of the given four alternatives after the statements,choose the one that describes the statements.
$A$ thin air film is formed by putting the convex surface of a plano-convex lens over a plane glass plate. With monochromatic light,this film gives an interference pattern due to light reflected from the top (convex) surface and the bottom (glass plate) surface of the film.
Statement $- 1$: When light reflects from the air-glass plate interface,the reflected wave suffers a phase change of $\pi$.
Statement $- 2$: The centre of the interference pattern is dark.

• A
  Statement $- 1$ is true,Statement $- 2$ is true,Statement $- 2$ is the correct explanation of Statement $- 1$.
• B
  Statement $- 1$ is true,Statement $- 2$ is true,Statement $- 2$ is not the correct explanation of Statement $- 1$.
• C
  Statement $- 1$ is false,Statement $- 2$ is true.
• D
  Statement $- 1$ is true,Statement $- 2$ is false.