In this word riddle, "Forward I am heavy, backward I am not." Who am I?

Introduction / Context:
This riddle is about reversing a word and noticing how its meaning changes completely. The phrase forward I am heavy points to a word that describes a large weight. The phrase backward I am not suggests that when the letters are reversed, the resulting word means the opposite, something light or simple. The classic answer is ton, which reversed becomes not. Together, these two words form a neat wordplay pair that fits the riddle perfectly.

Given Data / Assumptions:

• The word refers to something heavy when read normally.
• When the letters are reversed, the new word means not.
• Options include Weight, Ton, Quintal, None of these and Rock.
• We assume standard English spellings and meanings.

Concept / Approach:
A ton is a large unit of weight used to measure heavy objects. When you reverse the letters t, o, n, you get n, o, t, which form the word not. Not expresses negation and is conceptually linked to something not being or not existing, fitting the idea of not heavy. This word pair is well known in English wordplay and is often used in riddles to show how a simple reversal can change the entire meaning of a term.

Step-by-Step Solution:
Step 1: Consider the clue forward I am heavy and think of common words associated with large weights. Step 2: Ton is a basic unit that literally means a very heavy amount, so it is a strong candidate. Step 3: Reverse the letters of ton to see what new word appears: t o n becomes n o t. Step 4: The reversed word not is a valid English word and is used to express the idea of no or the absence of something. Step 5: Interpret backward I am not as a direct reference to this reversed word. Step 6: Confirm that other options like Weight, Quintal or Rock do not form meaningful or appropriate words when reversed. Step 7: Conclude that Ton is the only option fitting both forward and backward clues exactly.

Verification / Alternative check:
Test another option for comparison. If you reverse Weight, you get thgiew, which is not an English word. Reversing Quintal gives latniuq, which again is not meaningful. Rock reversed is kcor, which does not read as a standard word. None of these therefore have the clever double meaning that ton and not share. This confirms that the riddle is specifically constructed around the ton and not pair, a favourite example in English language puzzles.

Why Other Options Are Wrong:
Weight: Describes heaviness but does not form a meaningful opposite when reversed.
Quintal: Also a unit of weight, but reversing it does not yield a separate English word.
None of these: This is incorrect because Ton satisfies the riddle in a very precise way.
Rock: A rock can be heavy, but rock spelled backwards is not a proper word with the meaning not.

Common Pitfalls:
A common mistake is to stop once you find any heavy related word and not check the reversal condition carefully. Another pitfall is to ignore the requirement that the reversed form must be a valid English word with a meaningful opposite sense. The best strategy is to test each candidate by writing it forward and backward. As soon as you see ton and not, the elegance of the solution becomes obvious and matches many similar riddles seen in English puzzle collections.

Final Answer:
The word that is heavy forward and not backward is Ton.