Answer:
a.Attractive

Explanation:
When it comes to charges, the charges which are alike repel each other and the charges which are different will attract each other.
Here, there is a proton and electron which are different particles hence, they will attract each other.
= Charge of electron and proton = 
r = Distance between them = 997 nm
k = Coulomb constant = 
Force is given by

The force of attraction between the particles will be 
Avogadro's number: 6.02 x 10^23 atoms is present in 1mol of a solid (i.e. 22, 400 cm3)
Hence, in 1 cm3, 6.02 x 10^23 /22400 atoms is present = 2 x 10 ^ 19 atoms.
The digestive system digests and makes nutrients out of food while the circulatory system distributes and circulates the nutrients i believe?
Answer : When a person applies force and covers distance then the person is doing work on an object.
Answer:
In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46.