U-238 has protons and146 neutrons. a particular isotope of plutonium has 94 protons, neutrons, and a mass number of 241. thorium- has 90 protons and 137 neutrons.

#1

so mass number = 238

mass number = protons + neutrons

given that

neutrons = 146

238 = protons + 146

protons = 92

#2

so mass number = 241

mass number = protons + neutrons

given that

Protons = 94

241 = 94 + neutrons

neutrons = 147

#3

A = mass number

Protons = 90

Neutrons = 137

A = protons + Neutrons

A = 90 + 137 = 227

We have that the missing Variables are

From the question we are told that

Generally

For U-238

Generally the equation for the mass Number  is mathematically given as

X=Protons Number+Neutrons Number

Therefore

238=P+146

P=92

Protons Number P=92

For isotope of plutonium

X=Protons Number+Neutrons Number

241=94+N

N=147

Neutrons Number N=147

For Thorium

X=Protons Number+Neutrons Number

X=90+137

X=227

mass Number

X=227

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