A boy of height 1.5 m with his eye level at 1.4 m stands before a plane mirror of length 0.75 m fixed on the wall. The height of the lower edge of the mirror above the floor is 0.8 m. Then :

Use the theorem for triangles that are comparable. Three triangles are created. One of the triangles is 1.4 meters tall, the other is 0.8 meters tall, and the third triangle is y meters tall. Equivalence triangles 1 and 2 and triangles 2 and 3 using the theory for comparable triangles. Therefore, determine y, the duration of the picture that the youngster is unable to perceive.

Let y represent the duration of the picture that the boy is unable to view.
The similar triangles theory tells us that

$\frac{y}{x_0}=\frac{0.8}{x+x_0}$
$\therefore y=\frac{0.8\times x_0}{x+x_0}\dots$(1)
Now, agthe theorem of the similar trianglees theorem,
$\frac{1.4}{x+x+x_0}=\frac{0.8}{x+x_0}$
$\therefore 1.4\times \left(x+x_0\right)=0.8\times \left(2x+x_0\right)$
$\therefore x_0=\frac{x}{3}$
Changing the above equation's order gives us,
$x=3\times x_0\dots \text{ (2) }$
Changing the equation now. (2) in the formula. (1) we obtain,
$y=\frac{0.8\times x_0}{3\times x_0+x_0}$
$\therefore y=\frac{0.8x_0}{4x_0}$

$\therefore y=0.2m$

He cannot see his feet, hence the length of the picture he cannot see in the mirror is 0.2 meters.

Hence, the correct answer is option C.