An element:

An element is a pure substance that cannot be broken down into simpler substances by chemical means. It consists of atoms with the same number of protons in their nuclei. Elements are the building blocks of matter and are represented by symbols on the periodic table.

a) One type of element:

Each element on the periodic table is unique and consists of only one type of atom. For example, oxygen (O), carbon (C), and gold (Au) are all elements that are made up of only one type of atom. These atoms have a specific number of protons in their nuclei, which defines their atomic number and distinguishes them from other elements.

b) Two or more types of element:

When two or more elements combine chemically, they form compounds. Compounds are substances composed of atoms of different elements bonded together in specific ratios. For example, water (H2O) is a compound consisting of two hydrogen atoms bonded to one oxygen atom. In this case, hydrogen and oxygen are two different types of elements that combine to form a compound.

c) Constant boiling point:

The boiling point of a substance is the temperature at which it changes from a liquid to a gas. Different substances have different boiling points, which depend on the strength of intermolecular forces between their molecules. However, for a specific substance, the boiling point remains constant under normal conditions (i.e., at a specific pressure).

The boiling point of an element can vary depending on its atomic structure and intermolecular forces. For example, helium (He) has a very low boiling point of -268.93°C, while tungsten (W) has a very high boiling point of 5,555°C. These boiling points are specific to each element and remain constant as long as the pressure and other external factors remain unchanged.

d) Has constant boiling point:

Every element has a specific boiling point, which remains constant for that particular element. This is because the boiling point is determined by the strength of intermolecular forces and the energy required to overcome these forces. Elements with similar atomic structures and intermolecular forces tend to have similar boiling points.

It is important to note that the boiling point can be affected by changes in pressure. At higher altitudes where the atmospheric pressure is lower, the boiling point of a substance decreases. However, within a specific pressure range, an element will have a consistent and constant boiling point.

In conclusion, an element is a pure substance consisting of only one type of atom. It can combine with other elements to form compounds. Each element has a specific boiling point that remains constant under normal conditions, as long as the pressure is constant.

Option a is correct