Which chemical element is found in group number 17, period number 3? Refer to appendix A.

Here are the answers to the multiple-choice questions:

QUESTION 1

1.1
The correct answer is B) Chlorine.
Chlorine (Cl) is located in Group 17 (halogens) and Period 3 of the periodic table.

1.2
The correct answer is C) Boron.
Beryllium (Be) is in Period 2. Among the options, Boron (B) is a semi-metal (metalloid) and is also found in Period 2.

1.3
The correct answer is A) The number of atoms of an element.
In a chemical formula, a subscript number indicates how many atoms of the element immediately preceding it are present in one molecule or formula unit. For example, in $\text{H}_2\text{O}$, the subscript '2' indicates there are two hydrogen atoms.

1.4
The correct answer is D) 2:1.
In a water molecule ($\text{H}_2\text{O}$), there are two hydrogen atoms for every one oxygen atom, making the ratio of hydrogen to oxygen 2:1.