Alkynes

Concept: Isotopes are different forms of the same chemical element. Their definition is based on the number of subatomic particles (protons and neutrons) in their nuclei. Step 1: Defining Isotopes Isotopes of a given element are atoms that have:
The same number of protons. The number of protons in an atom's nucleus defines the element and is called the atomic number (Z).
A different number of neutrons. Because they have the same number of protons but a different number of neutrons, isotopes of an element will have:
The same atomic number (Z).
A different mass number (A), since Mass Number = (Number of Protons) + (Number of Neutrons).
Nearly identical chemical properties, as chemical properties are primarily determined by the number of electrons (which equals the number of protons in a neutral atom).
Slightly different physical properties (like density or rate of diffusion) due to the difference in mass. Step 2: Analyzing the options
(1) mass number: Incorrect. Isotopes have different mass numbers because they have different numbers of neutrons. For example, Carbon-12 ( ) has a mass number of 12 (6 protons + 6 neutrons), while Carbon-14 ( ) has a mass number of 14 (6 protons + 8 neutrons).
(2) atomic weight: Atomic weight (or relative atomic mass) of an element is the weighted average of the masses of its naturally occurring isotopes. Individual isotopes have different atomic masses. The term "atomic weight" usually refers to the element as a whole, not a specific isotope in comparison to another isotope. However, different isotopes do have different individual masses.
(3) atomic number: Correct. By definition, all isotopes of a particular element have the same number of protons, and thus the same atomic number. This is what makes them the same element.
(4) molecular weight: This term applies to molecules (combinations of atoms), not individual atoms or isotopes in this context. Therefore, isotopes of an element have the same atomic number.

Concept: Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon. They are classified into alkanes, alkenes, alkynes, and aromatic hydrocarbons based on the types of bonds between carbon atoms. Each class has a general formula. Step 1: Recall the general formulas for different types of acyclic hydrocarbons
Alkanes: These are saturated hydrocarbons containing only single bonds between carbon atoms. Their general formula is (where ). Example: Methane ( , n=1), Ethane ( , n=2).
Alkenes: These are unsaturated hydrocarbons containing at least one carbon-carbon double bond ( ). For acyclic alkenes with one double bond, their general formula is (where ). Example: Ethene ( , n=2), Propene ( , n=3).
Alkynes: These are unsaturated hydrocarbons containing at least one carbon-carbon triple bond ( ). For acyclic alkynes with one triple bond, their general formula is (where ). Example: Ethyne (Acetylene, , n=2), Propyne ( , n=3). Step 2: Identify the general formula for an alkyne Based on the definitions, the general formula for an alkyne (with one triple bond and no rings) is . Step 3: Analyzing the options
(1) : This is the general formula for Alkanes.
(2) : This is the general formula for Alkynes (with one triple bond). Correct.
(3) : This is the general formula for Alkenes (with one double bond) or Cycloalkanes.
(4) : This formula does not correspond to a stable neutral hydrocarbon series. (For example, if n=1, , which is not standard). Therefore, the general formula of an alkyne is .