Does that mean i'm wrong if i say this?
... A nucleus is unstable when oxidation or reduction is taking place in the nucleus. This disrupts the outer shell (since it is either gaining or losing electrons) and hence, makes the nucleus unstable.
That is very wrong.
Oxidation and reduction do not occur in the nucleus. Redox processes involve the gain or loss of electrons from the electron cloud. Remember that the cloud surrounds the nucleus but never comes in contact with it. The dissruption to the outer shell results in an ion with more or less electrons compared to the neutral atom. An ion is, depending on the element, a stable entity.
You should have written something along the lines of:
The nucleus contains two types of particle, a positively charged proton which determines the element, and an uncharged neutron which determines the isotope of the element.
A stable nucleus usually satisfies one of two conditions:
1. Protons and neutrons in approximately equal numbers from Z = 1 (hydrogen) up to Z = 20 (Calcium).
2. From Z = 21 (Scandium) to Z = 83 (Bismuth) the ratio of protons to neutrons gradually increases upto approximately 1:1.5.
Thus an unstable nucleus is one which deviates largely from the two conditions above.
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If space remains you may also like to mention that
2H contains a stable nucleus despite a p:n of 1:2.
