Molecules: when atoms join up

Tests: 4 of 10 right · Exam: 3 of 4 right · Kind: ★ · Understood: 8 of 14 · Run: 2026-10-18, commit f3c23ea72

Lesson 3 of the chemistry course of Mova's primary school, as Mova's small model took its tests: it had read this lesson and the ones before it and learned from their exercises. Each test shows the options in the order the student saw them, its choice, the right answer, the score of every option and why it chose. The lesson itself, sentence by sentence with trees and pragmatics: the lesson in the corpora.

Every question of this lesson and each of its options parsed by Mova, with trees and pragmatics: the lesson's questions in the corpora.

Test 1 · ★ · right ✓

Your friend says: "Water is made of two gases, so it should be a gas too." What is the answer?

1. Water is only part hydrogen, mostly sand — no support
2. Water is secretly a gas that is only pretending to be wet — no support
3. She is right, water is always a gas — no support
4. Joined atoms make a new substance with new behaviour — ← Mova's choice · ✓ the right answer · score 8

Why: It took the question to ask which statement is true. It chose option 4 with score 8, the only option with support. Its support: lesson 2, line 1: «An element is a substance made of only one kind of atom: gold is only gold atoms, oxygen only oxygen atoms.», reached through the remembered sentence the question matched. What matched: the same action «make» (+4); the same thing acted on «substance» (+4). · the question and its options parsed, with trees and pragmatics

Test 2 · ★ · right ✓

"Is the carbon in an oak tree from stuff animals breathed out ages ago?" Best answer?

1. No, all tree carbon comes up from the soil through the roots — no support
2. Partly yes, trees build wood from carbon dioxide in the air — ← Mova's choice · ✓ the right answer · score 3
3. Only if the animals lived in the tree — no support
4. No, trees make all their carbon out of sunlight — no support

Why: It took the question to ask which statement is true. It chose option 2 with score 3, the only option with support. Its support: lesson 3, line 9: «Plants take in carbon dioxide and use it to build sugar and wood.», reached through the same lesson line as the sentence the question matched. What matched: the same action «build» (+2); the same thing acted on «sugar» (+2). Against it: a different doer (counts against) (-1). · the question and its options parsed, with trees and pragmatics

Test 3 · ★ · right ✓

In a cartoon, a lab-made lemon flavour is called "fake poison" though its molecule is exactly the same as the fruit's. What's wrong?

1. Fruit molecules are always safer — no support
2. Nothing is wrong, because molecules made in labs are always poisonous to eat — score 4
3. A molecule is the same whether a plant or a lab made it — ← Mova's choice · ✓ the right answer · score 8
4. Only plants can make real molecules — score 3

Why: It took the question to ask which statement is true. It chose option 3 with score 8, against 4 for the next best. Its support: lesson 1, line 19: «When ice melts, the same water molecules (a molecule = a small group of atoms joined together) are there before and after; melted ice weighs the same as the ic…», reached through the remembered sentence the question matched. What matched: the same doer «same water molecules» (+4); the same property (+2); the same light verb (be, have, do, get, go) (+2). · the question and its options parsed, with trees and pragmatics

Test 4 · ★ · wrong ✗

Your gran says: "Natural is always safe, artificial is always bad." Put her right.

1. Only water is ever safe — ← Mova's choice · no support
2. She is right, because nature never makes any poisons, only people in factories do — no support
3. Some natural things like deadly nightshade are poisonous; what matters is which and how much — ✓ the right answer · no support
4. Artificial things are always the safest — no support

Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics

Test 5 · ★ · wrong ✗

How does a two-metre DNA molecule fit inside a tiny cell?

1. It is folded in half only twice — ← Mova's choice · score 8
2. It is extremely thin and tightly coiled and packed — ✓ the right answer · no support
3. It sticks out of the cell like a long tail — no support
4. It is cut into pieces and thrown away — score 8

Why: It took the question to ask what something is like. It chose option 1 with score 8, tied with another option at 8 (the first shown, or the one claiming less beyond what it knows, wins). Its support: lesson 3, line 6: «A molecule is a group of atoms joined together; a water molecule (H2O) is two hydrogen atoms joined to one oxygen atom.», reached through the remembered sentence the question matched. What matched: the same doer «molecule» (+4); the same thing acted on «group» (+4). The right option, 2, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics

Test 6 · ★ · wrong ✗

"my brother says atoms in a ball-and-stick model are really red and white balls" What is the truth?

1. He is right, oxygen atoms really are red and hydrogen atoms are white — no support
2. Real atoms are all black — no support
3. The colours are only a custom; real atoms are not coloured balls — ✓ the right answer · no support
4. Atoms are white until they join up — ← Mova's choice · score 8

Why: It took the question to ask which statement is true. It chose option 4 with score 8, the only option with support. Its support: lesson 3, line 1: «Atoms rarely stay alone: they join up into groups called molecules, a bit like Lego bricks clicking together.», reached through the remembered sentence the question matched. What matched: the same action «join up» (+4); the same doer «atoms» (+4). The right option, 3, found no support in what it remembers. · the question and its options parsed, with trees and pragmatics

Test 7 · ★ · right ✓

What would happen if you tried to separate iron sulphide back into iron and sulphur with a magnet?

1. The compound would explode — no support
2. It would not work, the atoms are joined — ← Mova's choice · ✓ the right answer · score 2
3. The sulphur would stick to the magnet — score 0
4. The iron would jump straight out onto the magnet — no support

Why: It took the question to ask what happens next. It chose option 2 with score 2, against 0 for the next best. Its support: lesson 3, line 13: «Mixed iron filings and sulphur powder can be separated with a magnet; after a teacher heats them, they form iron sulphide, which the magnet no longer picks out.», reached through what followed the sentence the question matched. What matched: the same doer «iron sulphide» (+4). Against it: a different action (counts against) (-2). · the question and its options parsed, with trees and pragmatics

Test 8 · ★ · wrong ✗

A struck match gives a sharp smell. Where does it come from?

1. The wood was always smelly inside, and the flame just lets it out — ← Mova's choice · no support
2. Your nose gets scratched by the flame — no support
3. Smoke is the only thing with no molecules — no support
4. New gas molecules made by the burning, which your nose senses — ✓ the right answer · no support

Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics

Test 9 · ★ · wrong ✗

"rusty nail weighs more?? rubbish, rust is crumbly" Is the claim right?

1. No, rust always weighs less, because bits of it crumble off — ← Mova's choice · no support
2. No, rust weighs nothing — no support
3. Yes, the rust has extra oxygen atoms from the air — ✓ the right answer · no support
4. Yes, because water makes nails grow — no support

Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics

Test 10 · ★ · wrong ✗

A sugar molecule has 45 atoms. Which atoms are they?

1. Sodium and chlorine, like salt — ← Mova's choice · no support
2. Carbon, hydrogen and oxygen — ✓ the right answer · no support
3. Iron, oxygen and a little sulphur — no support
4. Only carbon, packed in a ring — no support

Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics

Exam question 1 · formal language · right ✓

Which of the following statements most accurately characterises a molecule?

1. A mixture of substances that may be separated by a magnet — no support
2. A particle visible to the unaided eye — no support
3. A group of two or more atoms joined together — ← Mova's choice · ✓ the right answer · score 5
4. A single atom deprived of its electrons — score 4

Why: It took the question to ask who or what does it. It chose option 3 with score 5, against 4 for the next best. Its support: lesson 3, line 6: «A molecule is a group of atoms joined together; a water molecule (H2O) is two hydrogen atoms joined to one oxygen atom.», reached through the same lesson line as the sentence the question matched. What matched: the same action «join» (+2); the same thing acted on «atoms» (+2); the same property (+1). · the question and its options parsed, with trees and pragmatics

Exam question 2 · formal language · right ✓

Identify the principal distinction between a mixture and a compound.

1. A mixture contains a single element only, whereas a compound contains a great many elements — no support
2. A compound is invariably liquid, whereas a mixture is invariably solid — no support
3. In a compound the constituent atoms are chemically joined, whereas in a mixture they are not — ← Mova's choice · ✓ the right answer · score 12
4. A compound may be separated by a magnet, whereas a mixture may not — no support

Why: It took the question to ask which statement is true. It chose option 3 with score 12, the only option with support. Its support: lesson 3, line 12: «In a mixture the ingredients are just mixed and can be separated; in a compound the atoms are joined and behave like a new substance.», reached through the remembered sentence the question matched. What matched: the same action «join» (+4); the same thing acted on «atoms» (+4); the same place «compound» (+4). · the question and its options parsed, with trees and pragmatics

Exam question 3 · formal language · right ✓

Select the response that is consistent with the established facts concerning the assertion that a beverage is "chemical-free".

1. All substances, beverages included, are composed of chemicals — ← Mova's choice · ✓ the right answer · no support
2. Only beverages manufactured in laboratories contain chemicals — no support
3. Chemicals are present solely in cleaning products — no support
4. Beverages from fruit contain no chemicals whatsoever — no support

Why: Nothing it remembers matched the question, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics

Exam question 4 · formal language · wrong ✗

It is given that an iron nail is exposed to water and air for several weeks. Ascertain the effect upon its mass.

1. The mass decreases to nothing — ← Mova's choice · no support
2. The mass decreases, iron having been destroyed — no support
3. The mass increases, oxygen having combined with the iron — ✓ the right answer · no support
4. The mass remains wholly unaltered — no support

Why: No option found support in what it remembers, so it guessed: it took the first option shown. · the question and its options parsed, with trees and pragmatics

This page in Markdown → https://md.mova.elamur.ai/free/en/school-run/chemistry/3-molecules-when-atoms-join-up/