ONE-EIGHTH STAGE 2023
ROUND 5 RIDDLES, ONE-EIGHTH STAGE
Achimota School: 66 points
Holy Child School: 41 points
Assin State College: 30 points
ROUND 5 - RIDDLE
RIDDLE
I am a material commonly used as a semiconductor.
I have uniquely high abrasion resistance and hence am used in sharpening metals.
I am also referred to as carborundum.
I am formed from two elements in Group 14.
Who am I?
ANSWER: Silicon carbide
EXPLANATION:
Silicon carbide (SiC) is formed from silicon and carbon, both Group 14 elements.
Its extreme hardness makes it a classic abrasive ("carborundum"), and it is also used as a wide-bandgap semiconductor in high-power/high-temperature electronics.
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PRACTICE QUESTIONS
1. RIDDLE:
I am a metalloid.
I am the second most abundant element in the Earth's crust.
I am the heart of computer chips.
My dioxide is sand.
I am in Group 14.
My symbol is Si.
Who am I?
ANSWER: SILICON
EXPLANATION:
Silicon is the semiconductor of electronics.
2. RIDDLE:
I am a white, very hard solid.
I am amphoteric.
Ruby and sapphire are coloured forms of me.
I am called corundum.
Bauxite is my impure hydrated form.
My formula is $Al_2O_3$.
Who am I?
ANSWER: ALUMINIUM OXIDE
EXPLANATION:
Alumina is amphoteric and very hard (corundum).
3. RIDDLE:
I am a metalloid.
Mendeleev predicted me as eka-silicon.
I was used in early transistors.
I am named after a European country.
I am in Group 14.
My symbol is Ge.
Who am I?
ANSWER: GERMANIUM
EXPLANATION:
Germanium confirmed Mendeleev's prediction of eka-silicon.
4. RIDDLE:
I am a metalloid.
I am the only non-metal in Group 13.
My fibres are very strong and light.
My oxide makes heat-resistant glass.
Borax is one of my compounds.
My symbol is B.
Who am I?
ANSWER: BORON
EXPLANATION:
Boron is the metalloid heading Group 13.
5. RIDDLE:
I am a very hard covalent solid.
I am called carborundum.
I am used as an abrasive on grinding wheels.
I am made of two Group 14 elements.
I am used in bulletproof vests.
My formula is SiC.
Who am I?
ANSWER: SILICON CARBIDE
EXPLANATION:
Silicon carbide has a diamond-like giant covalent structure.
6. RIDDLE:
I am a compound semiconductor.
I am made of a Group 13 element and a Group 15 element.
I am used in solar cells on satellites.
I make red LEDs and laser diodes.
Electrons move through me faster than through silicon.
My formula is GaAs.
Who am I?
ANSWER: GALLIUM ARSENIDE
EXPLANATION:
GaAs is a fast semiconductor used in LEDs and lasers.