<span>c) convection currents in the mantle </span>
Answer:

Explanation:
From the question we are told that:
Distance of wall from CD 
Second bright fringe 
Let
Strontium vapor laser has a wavelength \lambda= 431 nm=>431 *10^{-9}m
Generally the equation for Interference is mathematically given by

Where



An object is in motion if its distance from another object is changing. An object is in motion if it changes position relative to a reference point. An reference point is a place or object used for comparison to determine if something is moving.
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The 3rd Quadrant is the lower left one on a graph,
where ' x ' and ' y ' are both negative.
Your picture is completely unrelated to this question.