Test: Basic Units Of Matter - Class 9 MCQ

• Molecules of compounds are not made up of the same type of atoms. They are actually made up of different types of atoms in definite proportions. This means that compounds like water (H₂O) and carbon dioxide (CO_{2>) consist of varying types of atoms.}

An atom can be defined as the smallest particle of an element, which can take part in chemical change or reaction and still retain the identity of the element. Notice that the atom is not the smallest particle of an element, as there are electrons, protons and neutrons which are smaller, but, it is the smallest which can be involved in chemical change and still retain the chemical properties of the element.

Chlorine is called Cl₂ because it is a diatomic molecule.
Diatomic means there are two atoms of the same elements in the molecules.
There are other diatomic molecules, such as hydrogen (H2), Nitrogen (N2), Oxygen (O2), Fluorine (F2), Chlorine (Cl2), Bromine (Br2), Iodine (I2).

Maharishi Kanad, an ancient Indian philosopher, proposed that matter could be divided into smaller particles until reaching an indivisible unit called "Parmanu." This idea helped in understanding how matter is composed of tiny building blocks that cannot be divided further.

A combination of atoms is called a molecule. We know that atoms of most of the elements are very reactive and cannot exist in the free state (as single atoms). This is not so with molecules. Molecules can exist in free state because they are very stable.

• Atoms of a given element are actually identical in mass and chemical properties. This means that all atoms of the same element have the same mass and behave in the same way chemically. It's like having a bunch of identical Lego blocks that are all the same size and shape. So, the statement is False because atoms of the same element are not different, but they are the same.

Argon is a Noble gas. Noble gases are not very reactive since they have a very stable electron configuration. It is only about 1% of the air in the atmosphere but it is more abundant than any other element on the Periodic Table behind Nitrogen and Oxygen.

Molecules of compounds are made up of different types of atoms in definite proportions, which means they always combine in fixed and specific ratios to form compounds.

The most fundamental building block of matter was a particle called the atom. Now we know that the atom is made of many smaller pieces, known as subatomic particles. Every atom contains a central core called the nucleus, made of particles called protons and neutrons.

• Hydrogen has one proton and one electron.
• It has the least mass among all elements, approximately 1.67 x 10^-27 kg.

Atomicity is the total number of atoms present in one molecule of an element or a compound. For example: one molecule of hydrogen (H₂) contains two atoms of hydrogen. Therefore, atomicity of hydrogen is 2. Simialrly, 1 molecule of O₃ contains 3 atoms. Therefore, its atomicity  is 3. molecule of Argon exist as Ar and hence its a monoatomic compound.

A geologist is a person who studies the earth. Geologists study the structure of the Earth, and they have found that it is made up of four main parts. The earth has a solid inner core, a liquid outer core, a mantle, and a crust.hence, option (D) is correct.

• The Law of Constant Proportions teaches us that chemical compounds, like water or ammonia, always keep the same elements in the same proportion by weight no matter where they come from or how they are made. This means that in water, for example, there will always be a fixed ratio of hydrogen to oxygen, and in ammonia, nitrogen to hydrogen will always be in a set proportion.

Atoms usually exist in two ways (1) in the form of molecules (2) in the form of ions 

A scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer (at IBM Zrich), the Nobel Prize in Physics in 1986. For an STM, good resolution is considered to be 0.1 nm lateral resolution and 0.01 nm (10 pm) depth resolution.With this resolution, individual atoms within materials are routinely imaged and manipulated. The STM can be used not only in ultra-high vacuum but also in air, water, and various other liquid or gas ambients, and at temperatures ranging from near zero kelvin to over 1000 DEGC.