The elements with atomic numbers 9, 17, 35, 53, 85 are all:

• A. Noble gases
• B. Halogens
• C. Heavy metals
• D. Light metals

The elements with atomic numbers 9, 17, 35, 53, and 85 are all classified as halogens. This group includes fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). Let’s break down what makes these elements unique and why they fit into this category.

What Are Halogens?

Halogens are a group of elements found in Group 17 of the periodic table. They are known for their high reactivity, particularly with alkali and alkaline earth metals, forming salts. The term "halogen" itself means "salt-former," which reflects their tendency to create ionic compounds.

Characteristics of Halogens

• Reactivity: Halogens are highly reactive, especially with metals. For example, sodium (Na) reacts vigorously with chlorine (Cl) to form sodium chloride (NaCl), or table salt.
• States of Matter: At room temperature, halogens exist in different states: fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid.
• Electronegativity: Halogens have high electronegativity values, meaning they have a strong tendency to attract electrons in chemical bonds.

Examples of Halogens

Let’s look at the specific elements you mentioned:

• Fluorine (F, atomic number 9): The most reactive of all elements, it is a pale yellow gas.
• Chlorine (Cl, atomic number 17): A greenish-yellow gas that is also very reactive, commonly used in disinfectants.
• Bromine (Br, atomic number 35): A reddish-brown liquid at room temperature, it is less reactive than chlorine but still quite reactive.
• Iodine (I, atomic number 53): A dark purple solid that sublimates to a violet gas, it is used in antiseptics and iodized salt.
• Astatine (At, atomic number 85): A rare and radioactive element, it is the least reactive of the halogens.

Why Not the Other Options?

Let’s clarify why the other options do not fit:

• Noble Gases: These elements (like helium and neon) are found in Group 18 and are known for their lack of reactivity due to having a full valence shell.
• Heavy Metals: This category includes metals like lead and mercury, which are not related to the halogens in terms of chemical properties.
• Light Metals: Elements such as lithium and aluminum fall into this category, but again, they do not share the characteristics of halogens.

In summary, the elements with atomic numbers 9, 17, 35, 53, and 85 are all halogens, distinguished by their reactivity and unique properties. Understanding these elements helps us appreciate their role in both chemistry and everyday life.