Explanation

• Stoicheion is a Greek word meaning element.
• The word is associated with the basic constituents of matter in ancient Greek philosophy.
• The word chemistry has a different origin, while the term element refers to a pure substance made of only one type of atom.

Last verified on 29-10-2026

Explanation

The balanced chemical equation is: 4Al + 3O₂ → 2Al₂O₃.

Molar mass of Al = 27 g/mol, so 27 g of Al = 1 mole.

According to the equation, 4 moles of Al react with 3 moles of O₂.

Therefore, 1 mole of Al requires ¾ mole of O₂.

Mass of O₂ = ¾ × 32 = 24 g.

Last verified on 29-10-2026

Explanation

• Foam is a colloid in which gas is dispersed in a liquid.
• Examples include soap foam and whipped cream.

Last verified on 29-10-2026

Explanation

• A neutron is approximately 1842 times heavier than an electron.
• An electron has a mass of approximately 9.11 × 10^-31 kg.
• A neutron has a mass of approximately 1.675 × 10^-27 kg.

Additional information:

• A proton is approximately 1836 times heavier than an electron.

Last verified on 29-10-2026

Explanation

• The azimuthal quantum number (l) determines the shape of an atomic orbital.

Additional information:

• The principal quantum number (n) determines the main energy level.
• It is related to the size of the orbital.
• The magnetic quantum number (m_l) determines the orientation of an orbital in space.
• The spin quantum number (m_s) describes the spin of an electron, which can be +1/2 or -1/2.

Last verified on 29-10-2026

Explanation

Molar mass of Na = 23 g/mol

Formula: moles = mass / molar mass

For 35g:

= 35 / 23 = 1.52 moles

Last verified on 29-10-2026

Explanation

Molar mass of ethyl alcohol (C2H5OH) = 46g/mol

46g = 1 mole

Molar mass of glucose (C6H12O6) = 180g/mol

180g = 1 mole

Both are 1 mole, so both contain Avogadro's number (6.022 x 10^23) of molecules.

Last verified on 29-10-2026

Explanation

For 12g of NH3:

Molar mass of NH3 = 17g/mol

Moles = 12 / 17 = 0.705 mol

1 molecule NH3 has 3 N-H covalent bonds.

Total moles of bonds = 0.705 x 3 = 2.117 mol

Number of bonds = 2.117 x 6.022 x 10^23

= 1.27 x 10^24 ≈ 1.2 x 10^24

So the answer is 1.2 x 10^24

Last verified on 29-10-2026

Explanation

• Alpha particles have high ionizing power.
• Because they are relatively massive and carry a +2 electric charge.

Additional information:

• Alpha particles have low penetrating power.
• It can be stopped by a sheet of paper or the outer layer of human skin.
• Alpha particles are helium nuclei containing two protons and two neutrons.

Last verified on 28-10-2026

Explanation

• The Pauli Exclusion Principle states that an orbital can contain a maximum of two electrons with opposite spins.
• No two electrons in the same atom can have identical values for all four quantum numbers.
• The two electrons in one orbital are represented by opposite spin arrows: ↑↓.

Last verified on 28-10-2026