The atomic symbol 206
82 pb represents lead-206 (pb-206), an isotope that has 82 protons and 124 neutrons. which atomic symbol could represent an isotope that undergoes radioactive decay to produce pb-206?
a. 238
92 u

b. 222
87 pb

c. 178
72 hf

d. 192
77 pb

Answer is: A. 238/92 U.

The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentration.

The decay chain of ²³⁸U is called the uranium series.

Decay start with U-238 and ends with Pb-206. There are several alpha and beta minus decays.

Alpha decay is radioactive decay in which an atomic nucleus emits an alpha particle (helium nucleus) and transforms into an atom with an atomic number that is reduced by two and mass number that is reduced by four.

In beta minus decay atomic number Z is increased by one, neutron is converted to a proton and an electron and an electron antineutrino.

the mantle

explanation:

earth is divided into three layers: the crust or the outermost layer on which we live; the underlying, middle layer - the mantle - and the core (the innermost layer of earth).