Answer:
²³⁸₉₂U has 146 neutrons
Step-by-step explanation:
To know which option is correct, we shall determine the number of neutrons in each case. This can be obtained as follow:
For ²⁴₁₂Mg:
Mass number (A) = 24
Proton number (P) = 12
Neutron number (N) =?
A = P + N
24 = 12 + N
Collect like terms
N = 24 – 12
N = 12
Thus, there are 12 neutrons in ²⁴₁₂Mg
For ⁷⁵₃₃As:
Mass number (A) = 75
Proton number (P) = 33
Neutron number (N) =?
A = P + N
75 = 33 + N
Collect like terms
N = 75 – 33
N = 42
Thus, there are 42 neutrons in ⁷⁵₃₃As
For ¹⁹₉F:
Mass number (A) = 19
Proton number (P) = 9
Neutron number (N) =?
A = P + N
19 = 9 + N
Collect like terms
N = 19 – 9
N = 10
Thus, there are 10 neutrons in ¹⁹₉F.
For ²³⁸₉₂U:
Mass number (A) = 238
Proton number (P) = 92
Neutron number (N) =?
A = P + N
238 = 92 + N
Collect like terms
N = 238 – 92
N = 146
Thus, there are 146 neutrons in ²³⁸₉₂U
Considering the options and the illustration made above, Only ²³⁸₉₂U has the correct number of neutrons written along side.