1. Which elements are known as d-block elements?

transition metals

alkali earth metals

halogens

alkali metals

The answer is Transition metals they are the d-block elements.

Explanation:

The transition metals are called d-block due to these elements have electrons in the outer orbital d.

Orbitals in atoms: The atoms have electrons that are negative charged particles moving around the nucleus. The electrons are distributed in orbitals, each orbital has an energy value and representations with letters the lowest energy orbital is s, then p, d and f.

The d-orbital due to its energetic value can hold up to 10 electrons and these elements are important due to they are required for many organic, inorganic, biological and technological process.

For example: a d-block element is the Iron Fe who has magnetic properties and it is required for the human body to form hemoglobin (protein needed for oxygen transport in cells.

The d-block elements are found in groups 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 of the periodic table.

So your answer is A) Transition metals