The best answer to go with is b
Answer:

Explanation:
From the question we are told that
The electric filed is
Generally according to Gauss law
=> 
Given that the electric field is pointing downward , the equation become

Here
is the excess charge on the surface of the earth
is the surface area of the of the earth which is mathematically represented as

Where r is the radius of the earth which has a value 
substituting values


So

Here
s the permitivity of free space with value

substituting values


The snail would travel 100mm
Each minutes is 25mm and it took 4 minutes
4 x 25 = 100
or
25+25+25+25=100
This is an example of sublimation where a substance goes directly from solid to a gas, skipping the liquid stage.