Quiz: First 30 Elements and Compounds — 4 questions

1. Which element has atomic number 26?

A. Manganese

B. Iron

C. Chromium

D. Cobalt

Answer: (B)

Explanation

Atomic number 26 corresponds to iron, whose symbol is Fe. Cobalt follows it at atomic number 27, while chromium and manganese have atomic numbers 24 and 25.

2. Which sequence correctly identifies the elements with atomic numbers 18, 19, and 20?

A. Argon, calcium, scandium

B. Argon, potassium, calcium

C. Chlorine, argon, potassium

D. Sulfur, chlorine, argon

Answer: (B)

Explanation

The elements at atomic numbers 18, 19, and 20 are argon, potassium, and calcium. The neighboring sequences shift the atomic-number positions or use elements from earlier in the list.

3. Which formula represents baking soda?

A. $\mathrm{NaOH}$

B. $\mathrm{NaClO}$

C. $\mathrm{NaHCO_3}$

D. $\mathrm{CaCO_3}$

Answer: (C)

Explanation

Baking soda is sodium bicarbonate, with the formula $\mathrm{NaHCO_3}$. $\mathrm{NaOH}$ is caustic soda, $\mathrm{CaCO_3}$ is limestone, and $\mathrm{NaClO}$ is bleach.

4. A household label shows the formula $\mathrm{CO}$. Which compound does this formula identify?

A. Carbon dioxide

B. Sodium bicarbonate

C. Calcium carbonate

D. Carbon monoxide

Answer: (D)

Explanation

The formula $\mathrm{CO}$ identifies carbon monoxide, also called stove poison in the listed compounds. Carbon dioxide has the additional oxygen atom and is written $\mathrm{CO_2}$.