First 30 Elements and Compounds Practice Quiz (4 questions)

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.

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.

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.

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 $\mathrm{CO_2}$.