Isotope Notation in Chemistry

Steps:

• Isotopes are atoms of the same element with the same atomic number but different mass numbers.
• Standard notation for an isotope is ^A Z, where A (superscript) is the mass number and Z is the element symbol.
• Examine choices: A uses superscript 1 before Q, indicating mass number 1 for element Q.
• Choices B, C, D use invalid symbols (_ , :) that do not denote mass number.

Why A is correct:

• Superscript notation (^1Q) follows the IUPAC standard for specifying the mass number of an isotope while keeping the element symbol Q.

Why the others are wrong:

• B (_1Q): Subscript denotes atomic number, specifying a different element, not an isotope of Q.
• C (,1Q): Comma is not a valid notation symbol in chemistry.
• D (:1Q): Colon is invalid and unrelated to isotope designation.

Final answer: A