In the group of noble gases, which element is considered the heaviest under normal conditions?

Introduction / Context:
Noble gases are a group of elements in the periodic table known for their very low chemical reactivity. They include helium, neon, argon, krypton, xenon and radon. One simple general knowledge question about these elements concerns their relative atomic masses and which noble gas is the heaviest. This is useful for understanding periodic trends and for answering basic chemistry questions in competitive examinations.

Given Data / Assumptions:

• The noble gases in the conventional list are helium, neon, argon, krypton, xenon and radon.
• Heavier elements in a group have higher atomic numbers and larger atomic masses.
• The question asks specifically for the heaviest noble gas among the commonly discussed ones.
• We ignore super heavy synthetic elements not covered in standard school syllabi.

Concept / Approach:
In the periodic table, noble gases are placed in group 18. As we go down a group, atomic number and atomic mass increase. Helium is at the top with the smallest mass, followed by neon, argon, krypton, xenon and finally radon at the bottom of the group. Therefore radon is the noble gas with the highest atomic mass among the commonly encountered elements. Although advanced research has created even heavier synthetic elements, general knowledge questions usually consider radon as the heaviest noble gas.

Step-by-Step Solution:
Step 1: List the noble gases in order: helium, neon, argon, krypton, xenon and radon. Step 2: Recall that moving down the group increases both atomic number and atomic mass. Step 3: Identify the noble gas at the bottom of the group as the heaviest. Step 4: Recognise that radon lies below xenon and krypton on the periodic table. Step 5: Choose radon from the given options as the correct answer.

Verification / Alternative check:
A quick check using approximate atomic masses helps. For example, helium has an approximate mass of 4, neon around 20, argon about 40, krypton near 84, xenon around 131 and radon higher still, with a mass value above xenon. Comparing these approximate values confirms that radon is heavier than krypton and xenon, so radon is the heaviest noble gas in the conventional list.

Why Other Options Are Wrong:
Helium, neon and krypton are located above xenon and radon in the periodic table, and each has a smaller atomic mass.
Xenon is heavier than krypton but is still above radon and therefore not the heaviest in the group.
Any noble gas that is not at the bottom of the group cannot be the heaviest among the commonly studied noble gases.

Common Pitfalls:
Students sometimes get confused between xenon and radon because both are heavier noble gases and are used in special applications. Another mistake is assuming that xenon is the heaviest simply because it is more familiar. Remember that in a group the elements become heavier as you move downwards. Keeping the vertical order of the noble gases in mind makes it easy to recall that radon is the heaviest among them.

Final Answer:
Among the commonly known noble gases, the heaviest element is radon.