Atomic numbers identify elements and trends

Steps:

• Total electrons equal atomic number, so Q (17 electrons) is chlorine and R (19 electrons) is potassium.
• Both in period 3: Q in group 17 (halogen), R in group 1 (alkali metal).
• Metallic character increases left to right across a period (R left of Q).
• Thus, R is more metallic than Q.

Why D is correct:

• Metallic character trend: increases from right to left across a period due to decreasing electronegativity and ionization energy.

Why the others are wrong:

• A: Q (nonmetal) and R (metal) form ionic, not covalent, compounds.
• B: Q (halogen) forms negative ions by gaining electrons.
• C: Q has 7 outer electrons; R has 1, so Q has more.

Final answer: D