Which of the following elements is generally considered non radioactive under normal conditions?

Introduction / Context:
Elements can be broadly classified into those with stable nuclei and those that are radioactive. Radioactive elements have unstable nuclei that spontaneously emit radiation in the form of alpha, beta or gamma rays. Many heavy elements such as uranium, thorium and plutonium are well known for their radioactivity. In contrast, lighter elements such as silicon or germanium are typically stable and non radioactive under normal conditions. This question tests whether you can distinguish a generally stable, non radioactive element from a group of mostly radioactive elements.

Given Data / Assumptions:

• Thorium, uranium and plutonium are actinide elements with large, unstable nuclei.
• Polonium is a heavy element that is highly radioactive.
• Germanium is a metalloid located in the p block, used in semiconductors.
• The question asks which element is generally non radioactive, meaning it has stable isotopes in nature.

Concept / Approach:
Radioactive elements often have no stable isotopes and undergo continuous radioactive decay. Uranium and thorium occur naturally as radioactive elements and are used as nuclear fuels. Plutonium is an artificial or semi artificial radioactive element produced in nuclear reactors. Polonium has no stable isotopes and is very radioactive. Germanium, on the other hand, is a lighter element that has several stable isotopes found in nature. The approach is to identify the element that belongs to the group of stable metalloids rather than to the group of heavy radioactive actinides or related elements.

Step-by-Step Solution:
Step 1: Recall that uranium (U) and thorium (Th) are well known radioactive elements found in ores and used as nuclear fuels. Step 2: Plutonium (Pu) is produced in nuclear reactors and is strongly radioactive, used in some nuclear weapons and fuel. Step 3: Polonium (Po) is another heavy element with no stable isotopes and strong radioactivity, historically used as a source of alpha particles. Step 4: Germanium (Ge) is a metalloid in the same group as silicon and has stable isotopes; it is used in semiconductors and optics. Step 5: Therefore, among the listed elements, germanium is generally considered non radioactive under normal conditions.

Verification / Alternative check:
Looking at isotope tables, germanium has several stable isotopes, including mass numbers such as 70, 72, 73, 74 and 76, which do not undergo radioactive decay. In contrast, uranium naturally exists as radioactive isotopes such as U 238 and U 235, thorium exists mainly as Th 232 and plutonium isotopes such as Pu 239 are created in reactors and are all radioactive. Polonium isotopes including Po 210 are also radioactive. Standard periodic table references and nuclear data summaries clearly classify uranium, thorium, plutonium and polonium as radioactive, while germanium is listed as having stable, non radioactive isotopes.

Why Other Options Are Wrong:
Option A, thorium, is radioactive and undergoes a decay series that eventually produces stable lead isotopes. Option B, polonium, is strongly radioactive and has been used as a source of alpha particles. Option D, plutonium, is a well known radioactive element associated with nuclear technology. Option E, uranium, is a naturally occurring radioactive element used as nuclear fuel. Only option C, germanium, represents an element that is generally non radioactive due to the presence of stable isotopes in nature.

Common Pitfalls:
Students sometimes assume that any heavy element is automatically radioactive and any lighter element is always stable, but there are exceptions at the boundaries. However, in this list the radioactive elements are well known and often mentioned in connection with nuclear energy or radiation hazards. To avoid confusion, it helps to remember that actinides such as uranium, thorium and plutonium are typically radioactive, while metalloids in the middle of the table such as germanium and silicon are usually stable. Keeping track of which elements commonly appear in discussions of radioactivity will also guide your choices in similar questions.

Final Answer:
The element that is generally non radioactive under normal conditions is Germanium (Ge), which has stable isotopes and is widely used as a semiconductor material.