Online Test: Periodic Classification of Elements | Class 10 Chemistry

Question 1 of 18

Dobereiner arranged similar elements in groups of:

two

three

eight

ten

Explanation: Dobereiner's classification grouped three similar elements into a triad.

Question 2 of 18

In Dobereiner's triad Ca, Sr, Ba, the atomic mass of Sr is close to the:

sum of Ca and Ba

average of Ca and Ba

difference of Ca and Ba

double of Ca

Explanation: The middle element's mass is the average of the other two.

Question 3 of 18

Newlands' Law of Octaves worked well only up to:

calcium

iron

copper

bromine

Explanation: Beyond calcium the law of octaves broke down.

Question 4 of 18

Mendeleev arranged the elements in increasing order of:

atomic number

atomic mass

valency

density

Explanation: Mendeleev's table used atomic mass and similar chemical properties.

Question 5 of 18

Eka-silicon predicted by Mendeleev was later discovered as:

scandium

gallium

germanium

argon

Explanation: Germanium filled the gap of eka-silicon, matching the predicted properties.

Question 6 of 18

Which element had no fixed position in Mendeleev's periodic table?

carbon

hydrogen

oxygen

sodium

Explanation: Hydrogen resembles both Group I (alkali metals) and Group VII (halogens).

Question 7 of 18

The scientist who established atomic number as the basis of classification was:

Newlands

Dobereiner

Moseley

Mendeleev

Explanation: Henry Moseley showed atomic number is more fundamental than atomic mass.

Question 8 of 18

The modern periodic law states that properties of elements are a periodic function of their:

atomic mass

atomic number

valency

number of neutrons

Explanation: The modern law is based on atomic number, not atomic mass.

Question 9 of 18

The number of vertical columns (groups) in the modern periodic table is:

7

8

16

18

Explanation: The modern table has 18 groups and 7 periods.

Question 10 of 18

An element with configuration 2, 8, 1 is placed in:

Period 2, Group 1

Period 3, Group 1

Period 1, Group 3

Period 3, Group 8

Explanation: Three shells means Period 3; 1 valence electron means Group 1 (sodium).

Question 11 of 18

The period number of an element is equal to the number of:

valence electrons

occupied shells

protons

neutrons

Explanation: The period number equals the number of shells in the atom.

Question 12 of 18

Elements in the same group have the same number of:

shells

valence electrons

neutrons

protons

Explanation: Same valence electrons give similar chemical properties within a group.

Question 13 of 18

As we go from left to right across a period, atomic size:

increases

decreases

stays constant

first decreases then increases

Explanation: Nuclear charge rises while shells stay fixed, so the atom shrinks.

Question 14 of 18

Down a group, the atomic size of elements:

increases

decreases

remains the same

becomes zero

Explanation: A new shell is added at each step, so size increases down a group.

Question 15 of 18

Metallic character across a period from left to right:

increases

decreases

stays the same

first increases then decreases

Explanation: Smaller size and stronger nuclear pull make electrons harder to lose, so metallic character decreases.

Question 16 of 18

The valency of an element with configuration 2, 8, 7 is:

7

1

8

2

Explanation: It needs 1 electron to complete the octet, so its valency is 8 - 7 = 1.

Question 17 of 18

Which of these is the most metallic?

Li

Na

K

Be

Explanation: K is lowest in Group 1, with the largest size, so it loses its electron most easily.

Question 18 of 18

The staircase region between metals and non-metals contains:

noble gases

alkali metals

metalloids

halogens

Explanation: Metalloids such as silicon and germanium lie between metals and non-metals.

Online Test — Periodic Classification of Elements