SSC CGL 2024 Tier-I · 25 September 2024, Shift 1 · General Awareness · Question 25 of 100

Text as printed on a candidate's response sheet for this shift; answer per SSC's tentative key as marked on that sheet. Solution last reviewed 10 September 2026.

Where this paper and its answers come from

SSC does not publish CGL question papers or a public answer key. The questions and options here are reproduced as printed on a candidate's own response sheet for this shift — the Commission's text, unchanged. Each answer is SSC's tentative key as marked on that sheet; SSC allowed challenges to it and never publishes a final key. The solutions are written by UnlockIAS.

According to Mendeleev's Periodic Table, which elements’ properties matched up remarkably well with eka-silicon?

(a)Scandium
(b)Gallium
(c)Titanium
(d)Germanium

Answer

Why

Correct — D. Eka-silicon was Mendeleev's name for the element missing one place below silicon, and it turned out to be germanium, isolated by Clemens Winkler in 1886.

The closeness of the match is what made the table famous: Mendeleev had set out the atomic mass, the density and the formula of the oxide for an element nobody had seen, and germanium fitted them.

Eka is Sanskrit for one, so eka-silicon reads as one place after silicon in the same group. That is option (d).

Why the others are wrong

(a)
Scandium — Scandium filled the eka-boron gap, found by Lars Nilson in 1879. It is one of Mendeleev's confirmed predictions, but not this one.
(b)
Gallium — Gallium filled the eka-aluminium gap, found by Lecoq de Boisbaudran in 1875. It was the first of the gap predictions to be confirmed, which is why it is the favourite wrong answer.
(c)
Titanium — Titanium was already a known element holding its own place in Mendeleev's table. It was never one of the empty slots, so nothing was predicted for it.

Concept

Mendeleev arranged the elements by increasing atomic mass and put the periodicity of properties ahead of a tidy sequence.

Where no known element fitted a slot he left the slot empty and described the element that would fill it, naming it with the Sanskrit prefix eka, meaning one.

Three of those gap predictions were confirmed in his lifetime: eka-aluminium as gallium in 1875, eka-boron as scandium in 1879 and eka-silicon as germanium in 1886. That accuracy is what won the table its acceptance.

Mendeleev's periodic law was stated in terms of atomic mass. The modern law rests on atomic number instead, after Moseley's work, which resolved the reversed pairs Mendeleev could not explain.

Key facts

Eka-silicon was Mendeleev's predicted element, discovered as germanium by Clemens Winkler in 1886.
Eka-aluminium was discovered as gallium in 1875 and eka-boron as scandium in 1879.
Eka is Sanskrit for one, and marks the element one place below the named element in the same group.
Mendeleev's periodic law was based on atomic mass, while the modern periodic law is based on atomic number.

Study next

Mendeleev's gap predictions and the anomalous pairs his table could not placeMoseley's work and the move from atomic mass to atomic numberNewlands' Law of Octaves and Dobereiner's triads

Common traps

Matching eka-silicon to gallium, which belongs to the eka-aluminium gap.
Choosing titanium because it sits near the metalloids, when titanium was already known and placed.

SSC works down the same list of predicted elements across shifts. The predicted atomic mass of eka-aluminium is asked on 19 Sep 2024, 12:30, General Awareness Q.18, and Newlands' Octaves on 19 Sep 2024, 16:00, General Awareness Q.20.

Related PYQs

No directly related past PYQ was found.