Question

An Atom's mass number is 210 and its atomic number is 85. How many neutrons does the atom have?
a.85
b.125
c.210
d.295

Answer 1

b.125                                                                                                                                   no of electrons=atomic no                                                                                          no of neutrons+no of electrons=mass no                                                                     no of neutrons=mass no-no of electrons                                                                        no of neutrons=210-85                                                                                                     no of neutrons=  125                                                                        

Answer 2

 

• There are 125 neutrons contained in the atom

• Atomic number can be regarded as the number of electrons in that atom.
• Hence, atomic number = 85, and number of electrons is 85

• Mass number is the addition of number of electrons as well as number of neutrons. It can be calculated as

• Mass number = ( number of electrons) + ( number of Neutron)

• ( number of Neutron) = (Mass number ) -  ( number of electrons)

Substitute the values

• ( number of Neutron) = ( 210 - 85)

= 125

Therefore, the correct option is B, which is  125 electrons

               Learn more at;   https://brainly.com/question/17306459