Alright, let's determine what element cesium-135 ([tex]\( _{55}^{135} Cs \)[/tex]) becomes after a beta decay. Here's a step-by-step explanation:
1. Understanding Beta Decay: In a beta decay, a neutron in the nucleus is transformed into a proton, while emitting a beta particle (an electron [tex]\( e^-\)[/tex]) and an antineutrino. This process increases the atomic number by 1 but keeps the mass number the same since neutrons and protons have nearly the same mass.
2. Initial Element:
- Cesium ([tex]\( Cs \)[/tex])
- Atomic Number (Number of Protons): 55
- Mass Number (Protons + Neutrons): 135
3. After Beta Decay:
- The atomic number increases by 1 because a neutron turns into a proton:
[tex]\[
55 + 1 = 56
\][/tex]
- The mass number remains the same because the total number of nucleons (protons and neutrons) does not change:
[tex]\[
135
\][/tex]
4. Identifying the New Element:
- The new element with an atomic number of 56 is Barium (Ba) according to the periodic table.
So, cesium-135 ([tex]\( _{55}^{135} Cs \)[/tex]) becomes barium-135 ([tex]\( _{56}^{135} Ba \)[/tex]) after beta decay.
Therefore, the correct answer is:
D. [tex]\( _{56}^{135} Ba \)[/tex]
