Questions Related to Science

More complex organisms cannot reproduce by regeneration because their bodies are made of many specialised cells and organs that depend on each other.
If a big part is cut, the body cannot rebuild all those complex organs again.

Regeneration in such organisms only helps in healing wounds, not making a whole new individual.

An organism benefits from spore formation because spores can survive harsh conditions like heat, dryness, or lack of food.
They are light and easily spread by wind or water, helping the organism spread to new places.
When conditions become favourable again, the spores grow into new organisms.

In binary fission, one organism splits into two equal parts, each becoming a new organism (like in amoeba).
In multiple fission, one organism divides into many daughter cells at the same time (like in Plasmodium).

So, binary fission produces two offspring, while multiple fission produces many in one go.

Variation is useful for a species because it gives different members different qualities, so if the environment changes, some of them can still survive.
But a single individual doesn’t always benefit from the variation it has — it might help, or it might not make any difference.
So variation helps the species continue, even if it doesn’t always help each individual.

DNA copying is important because it passes the parent's traits to the offspring.  OR  DNA copying is important because it gives the new baby the same instructions as the parents.

It helps the new cell or organism know how to grow and work.
Small changes during copying also create differences between individuals

In one molecule of H₂SO₄ (sulphuric acid):

Hydrogen (H) = 2 atoms
Sulphur (S) = 1 atom
Oxygen (O) = 4 atoms

Total atoms = 2 + 1 + 4 = 7 atoms
There are 7 atoms in one molecule of H₂SO₄.

Oxygen (O₂) is a diatomic gas.

To calculate the formula unit mass of calcium chloride (CaCl₂):

Atomic mass of Ca = 40
Atomic mass of Cl = 35.5

Formula unit mass = 40 + (2 × 35.5) = 40 + 71 = 111 u
So Formula unit mass of CaCl₂  is  111 u

There are 6.022 × 10²³ atoms in exactly  12 g of carbon.
This number is known as the Avogadro number, and 12 g of carbon represents 1 mole of carbon atoms.

The Latin name of  sodium is Natrium.
The Latin name of  mercury is Hydrargyrum.

Molecular mass is the sum of the atomic masses of all the atoms present in a molecule. It represents the total mass of one molecule of a substance and is expressed in atomic mass units (amu).

Example:
The molecular mass of water (H₂O) = (2 × 1) + 16 = 18 amu.

The number 6.023 × 10²³ is called the Avogadro number or Avogadro constant. It represents the number of particles (atoms, molecules, or ions) present in one mole of a substance.

The term used to represent the mass of 1 mole molecules of a substance is molar mass. It is expressed in grams per mole (g/mol).

The law of conservation of mass was given by Antoine Lavoisier in 1774.

He stated that mass can neither be created nor destroyed in a chemical reaction. This means that the total mass of the reactants is always equal to the total mass of the products.

Lavoisier proved this law through careful experiments, showing that even when substances change form during a reaction, their total mass remains the same.

The complete symbol of an atom is written as:

A (mass number)
Z (atomic number)
X (symbol of element)

Example: For sodium, atomic number = 11 and mass number = 23, the symbol is ²³₁₁Na.

The three isotopes of hydrogen are represented as:

1. Protium (¹₁H) – 1 proton and no neutron
2. Deuterium (²₁H) – 1 proton and 1 neutron
3. Tritium (³₁H) – 1 proton and 2 neutrons

Atomic number: Number of protons = 3
Mass number: Number of protons + Number of neutrons = 3 + 4 = 7
Valency: Atomic number 3 means the element is Lithium (Li). Its electronic configuration is 2, 1, so it has 1 valence electron -> Valency = 1.

Helium has zero valency because its outermost shell is completely filled with 2 electrons. It does not need to gain, lose, or share any electrons to become stable.
That’s why helium is chemically inactive and has valency = 0.

From the symbol ³²₁₆S:

i)  Atomic number of sulphur = 16
ii) Mass number of sulphur = 32
iii) Electronic configuration of sulphur = 2, 8, 6

The three subatomic particles are:

1. Proton (p⁺): Charge = +1, Relative mass = 1
2. Neutron (n⁰): Charge = 0, Relative mass = 1
3. Electron (e⁻): Charge = –1, Relative mass = 1/1836 (almost zero)