Chemistry Mid-Semester Exam 2024/2025

What defines an element?

• A substance composed of two or more types of atoms

• A substance composed of only one type of atom

• A combination of metals and nonmetals

• A substance that contains only molecules

Which of the following is an example of a mixture?

• Pure water (H₂O)

• Air

• Table salt (NaCl)

• Carbon dioxide (CO₂)

What defines a compound?

• A pure substance composed of only one type of atom

• A substance made of two or more elements chemically combined

• A mixture of two or more metals

• A liquid substance that dissolves metals

Which of the following is a compound?

• Sodium (Na)

• Water (H₂O)

• Helium (He)

• Gold (Au)

What is the charge of an electron?

• Positive (+)

• Negative (-)

• Neutral (0)

• Double negative (- -)

If an atom has 8 protons and 8 neutrons, what is its atomic mass?

• 8

• 16

• 24

• 32

What is the charge of a neutron?

• Positive (+)

• Negative (-)

• Neutral (0)

• Double positive (+ +)

An element with an electronic configuration of 2,8 belongs to which period?

• Period 1

• Period 2

• Period 3

• Period 4

What is the chemical symbol for helium?

• H

• He

• Hm

• Hl

What is the chemical symbol for lithium?

• Li

• L

• Lt

• Lu