a)When silver nitrate comes in contact with skin, it is reduced to white color metallic silver.In most cases, a black stain appears due to formation of finely divided silver which has black color.

The black color is due to the decomposition of the Ag+ ion into Ag, silver. Silver nitrate will slowly decompose with the silver ion reverting to elemental silver. The microscopic particles of silver are so small that they absorb light instead of reflecting it, and so appear black, instead of silver....

Here, the given equation of parabola is y²= 8x.

The equation of tangent to the parabola y²=8x is,

y= mx + 2/m

This tangent passes through the point (-2, 3)

So, 3 = -2m + 2/m

or, 3m + 2m² = 2

or, 2m²+3m - 2= 0

or, 2m² + (4 - 1)m -2 = 0

or, 2m² + 4m - m - 2 = 0

or, 2m(m + 2) - 1(m+2) = 0

or, (m + 2) (2m - 1) = 0

Either, Or,

m = -2 m = 1/2

Required angle is,

the symbols used in the story are:

1. house and shops- it symbolizes Aksionov's family and material possessions
2. nightmare-it symbolizes a bad omen.
3. blood-stained knife- it indicates Aksionov's lack of control over his fate.
4. the prison- Aksionov's pain and subsequent mystical transformation are symbolized by the prison.
5. the book(the lives of the saints)- gives an impression of religiosity.