The atomic number of lithium is 3. how many neutrons does an atom of lithium have if it is represented by the symbol shown below?

7li
a. 2 neutrons
b. 13 neutrons
c. 4 neutrons
d. 7 neutrons

C. 4 neutrons

Explanation:

General representation of an element is given as:  

where,

Z represents Atomic number

A represents Mass number

X represents the symbol of an element

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

A = Mass number = Number of protons + Number of neutrons = 7

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

Z= Atomic number = Number of electrons = Number of protons = 3

7 = 3 + Number of neutrons

Number of neutrons  = 4

Thus there are 4 neutrons.

the potential energy of the reactants is 200j.

from the energy diagram, the energy of the product formed is 350j; this means that, this reaction is an endothermic reaction, because it absorbs energy from its environment.

2b2t

explanation:

2b2t