IMO Practice Test — Periodic Classification of Elements
13 Questions • 15 min • Olympiad level
15:00
Question 1 of 13
An element X is in Period 3 and Group 16. Its electronic configuration is:
2, 8, 6
2, 8, 16
2, 6, 8
2, 8, 8, 6
Explanation: Period 3 means 3 shells; Group 16 means 6 valence electrons, giving 2, 8, 6 (sulphur).
Question 2 of 13
Two elements P (2, 8, 1) and Q (2, 8, 7) combine. The formula and bond type of the compound are:
PQ, ionic
PQ2, covalent
P2Q, ionic
PQ, covalent
Explanation: P loses 1 electron, Q gains 1, so they form PQ (like NaCl), an ionic compound.
Question 3 of 13
Which sequence shows correct decreasing atomic size?
Na > Mg > Al > Si
Si > Al > Mg > Na
Mg > Na > Si > Al
Al > Si > Na > Mg
Explanation: Across period 3 size decreases left to right: Na > Mg > Al > Si.
Question 4 of 13
An element has 2 electrons in its outermost shell. It is most likely a:
non-metal of Group 16
metal of Group 2
noble gas
halogen
Explanation: Two valence electrons (and losing them) is typical of a Group 2 metal.
Question 5 of 13
Down Group 17 (F, Cl, Br, I), the non-metallic character:
increases
decreases
stays the same
first increases then decreases
Explanation: Atomic size increases down the group, so the pull on electrons weakens and non-metallic character decreases.
Question 6 of 13
An element with atomic number 18 is best described as:
a reactive metal
a reactive non-metal
an inert noble gas
a metalloid
Explanation: Z = 18 gives 2, 8, 8 (argon), a noble gas with a complete octet, so it is inert.
Question 7 of 13
Elements A (Z = 11) and B (Z = 19) belong to the same group because both have:
the same number of shells
1 valence electron
the same atomic mass
7 valence electrons
Explanation: Na (2,8,1) and K (2,8,8,1) each have 1 valence electron, so both are in Group 1.
Question 8 of 13
Which property remains the same on moving down a group?
atomic size
valency
metallic character
number of shells
Explanation: Valency depends on valence electrons, which stay constant down a group.
Question 9 of 13
An oxide of an element is acidic. The element is most likely located:
on the far left of a period
on the right of a period (non-metal)
at the bottom of Group 1
in the metalloid staircase only
Explanation: Non-metals (right side of a period) form acidic oxides, while metals form basic oxides.
Question 10 of 13
If an element forms an ion M2+ and is in Period 4, its atomic number is:
12
20
18
38
Explanation: M2+ means 2 valence electrons (Group 2); Period 4 Group 2 is calcium, Z = 20 (2, 8, 8, 2).
Question 11 of 13
Across period 3, the element with the highest valency with respect to oxygen is:
Na
Mg
Si
Cl
Explanation: Valency rises to a maximum of 4 at silicon (SiO2) in the middle of the period.
Question 12 of 13
Element X loses electrons easily and element Y gains electrons easily. Compared on the same period, X is to the ____ of Y:
right
left
directly above
directly below
Explanation: Electron-losing metals lie on the left; electron-gaining non-metals lie on the right, so X is to the left of Y.
Question 13 of 13
Three elements have configurations 2, 8, 8; 2, 8, 8, 1; 2, 8, 7. Their correct identity order (noble gas, metal, non-metal) is:
Ar, K, Cl
K, Ar, Cl
Cl, K, Ar
Ar, Cl, K
Explanation: 2,8,8 = argon (noble gas); 2,8,8,1 = potassium (metal); 2,8,7 = chlorine (non-metal).