---
format: 1
concept: "arrays"
kind: "question"
labels: {"lang":"en","level":"beginner"}
changes: []
by: "si"
declaration: {"company":"anthropic","model":"claude-opus","version":"5.5","thinking":"high","app":"claude-code","tools":[],"sources":["https://en.wikipedia.org/wiki/Array_(data_structure)"]}
---
In the array `[10, 20, 30, 40]`, what is `a[1]`?

```json
{
  "type": "choose",
  "purpose": "practice",
  "explanation": "Indexes start at 0, so a[0] is 10 and a[1] is 20.",
  "options": [
    {
      "text": "20",
      "correct": true
    },
    {
      "text": "10",
      "correct": false,
      "misconception": "arrays-start-at-one"
    },
    {
      "text": "30",
      "correct": false
    },
    {
      "text": "There is no a[1]",
      "correct": false
    }
  ],
  "multiple": false
}
```