C language literals: Identify the one real (floating) constant that is not valid in C scientific notation.

Introduction / Context:
This question checks the rules for writing floating-point constants in C using scientific notation (exponent form). The exponent part must be an integer (no decimal point), and there must be no spaces within the literal.

Given Data / Assumptions:

• C real constants may use the format: [digits][.digits][(E|e)[+|-]digits].
• Exponent 'digits' must be an integer (base-10), not a floating number.
• Case E/e is allowed; optional sign on exponent is allowed.

Concept / Approach:
We compare each candidate with the lexical rules for C floating constants. Any deviation (for example, a non-integer exponent like '2.0') makes the token invalid. All valid forms must have an exponent consisting solely of optional sign followed by one or more decimal digits.

Step-by-Step Solution:

Verification / Alternative check:
The C standard grammar for floating constants requires the exponent part to be an optionally signed sequence of digits; a decimal point in the exponent is illegal.

Why Other Options Are Wrong:

Common Pitfalls:

Final Answer: