Question

A neutral atom of uranium (U) has 146 neutrons and a mass number of 238. How many protons does it have?

Answer 1

Answer:

Explanation:

One

I've never heard of a mass defect before you asked this question. Interesting concept.

Givens

Number of neutrons =207 - 82 = 125

Number of protons =  82

The amu of a proton is 1.00728

The amu of a neutron is 1.00866

Solution

Find out the actual mass of the Lead atom

Actual mass = 82*1.00728 + 125*1.00866

Actual mass = 208.67946

The mass defect = 208.67946 - 207 = 1.67946

That is the proper way to calculate mass defect.

Apparently the way you are supposed to do it is

Mass defect = 208.67946 - 206.975897= 1.703563 which means that C is the closest answer. You will have to look at your notes to see if amu for protons and neutrons are what I used.

Two

The number of protons is the number of Uranium on the periodic table.

92 protons. 92 comes from the position on the periodic table.

You can get the same thing by Taking its relative mass (238) and subtracting the neutrons (146) which is 238 - 146 = 92

Answer 2

Answer:

92 protons

Explanation:

The mass number is 238 , so the nucleus has  238  particles in total, including 146 neutrons.  So to calculate the number of neutrons we have to subtract:  238  −  146  =  92