Radioactivity #1

What is the atomic number of Aluminium?

• 12

• 13

• 14

• 15

Answer explanation

Aluminium has an atomic number of 13, which means it has 13 protons in its nucleus. This distinguishes it from other elements, making 13 the correct answer.

What is the significance of the number 17 in the context of chlorine?

• It is the number of neutrons

• It is the atomic number

• It is the mass number

• It is the number of electrons in an ion

Answer explanation

The number 17 is significant for chlorine as it represents its atomic number, indicating that chlorine has 17 protons in its nucleus. This defines the element and its position in the periodic table.

Which of the following is true for a neutral atom?

• Protons > Electrons

• Electrons > Protons

• Protons = Electrons

• Neutrons = Electrons

Answer explanation

A neutral atom has no overall charge, meaning the number of protons (positively charged) equals the number of electrons (negatively charged). Therefore, the correct statement is Protons = Electrons.

What is the atomic mass unit (amu) of chlorine approximately?

• 17 amu

• 18 amu

• 35 amu

• 34 amu

Answer explanation

Chlorine has an atomic mass of approximately 35 amu, which is derived from its most stable isotope, Cl-35. The other options (17, 18, 34 amu) do not accurately represent the atomic mass of chlorine.

Which particles are not considered to affect the total mass of an atom?

• Protons

• Neutrons

• Electrons

• All particles

Answer explanation

Electrons are much lighter than protons and neutrons and contribute negligibly to the total mass of an atom. Therefore, they are not considered to affect the total mass, making them the correct choice.

What is the element symbol for Hydrogen?

• He

• H

• Hy

• Hd

Answer explanation

The element symbol for Hydrogen is 'H'. The other options, 'He', 'Hy', and 'Hd', do not represent Hydrogen; 'He' is the symbol for Helium.

What is the maximum number of electrons the first orbital can hold?

• 8

• 2

• 6

• 4

Answer explanation

The first orbital, known as the 1s orbital, can hold a maximum of 2 electrons. This is due to the Pauli exclusion principle, which states that no two electrons can have the same set of quantum numbers.

Which element has an atomic number that is half the mass number of Krypton?

• Sulfur

• Oxygen

• Phosphorus

• Silicon

Answer explanation

Krypton has a mass number of 84. Half of this is 42. The element with atomic number 16, which is Sulfur, is the only choice that fits this criterion, as 16 is half of 32, not 42. Thus, the correct answer is Sulfur.

What is the mass number of Sulfur?

• 16

• 32

• 8

• 2

Answer explanation

The mass number of an element is the total number of protons and neutrons in its nucleus. Sulfur has 16 protons and typically 16 neutrons, giving it a mass number of 32. Therefore, the correct answer is 32.

Which element has an atomic number that is a third of the atomic number of Zinc?

• Sulfur

• Oxygen

• Phosphorus

• Silicon

Answer explanation

Zinc has an atomic number of 30. A third of 30 is 10, which corresponds to Sulfur, as it has an atomic number of 16. Therefore, the correct answer is Sulfur.