Question

What is the symbol for the nucleus remaining after $ _{20}C{a^{42}} $ undergoes $ \beta $ -emission?
(A) $ _{21}C{a^{42}} $
(B) $ _{20}S{c^{42}} $
(C) $ _{21}S{c^{42}} $
(D) $ _{21}S{c^{41}} $

Answer 1

Hint: Some unstable nucleus undergoes decay or decomposition to form a stable nucleus and the $ \beta $ particle by emitting radiation. That nucleus exhibiting radioactive emission can be called a radioactive nucleus and the process is known as $ \beta $ decay or $ \beta $ emission.

Complete answer:
The nucleus is a positively charged particle and contains two types of subatomic particles called protons and neutrons. Protons are positively charged subatomic particles and neutrons are zero charged subatomic particles. Due to the presence of protons the nucleus is positively charged.
Some of the unstable nucleus undergoes decay or decomposition to form a stable nucleus. The stable nucleus can be called the daughter nucleus. $ \beta $ -emission is the process of the emission of an electron, anti-neutrino and stable nucleus.
The $ {\beta ^ - } $ decay is one of the types of $ \beta $ -emission. The calcium is the element with atomic number $ 20 $ and mass number is $ 42 $ . The nucleus remaining after the calcium undergoes $ \beta $ -emission will be the element with the same mass number, but the protons will be added. Thus, the new element formed will be scandium with mass number $ 42 $ and the atomic number will be $ 21 $ .
Thus, the symbol will be $ _{21}S{c^{42}} $ . Option C is the correct one.

Note:
There are two types of $ \beta $ -emission. The $ {\beta ^ - } $ decay is one type and $ {\beta ^ + } $ decay is the second type. The given nucleus undergoes $ {\beta ^ - } $ decay to form an electron and antineutrino. The antineutrino will have a neutron. The mass number will be the same for both of the parent and daughter nucleus.