explanation

lib/data/default_deck.dart

@@ -17,18 +17,21 @@ class DefaultDeck {
         prompt: 'What is the capital city of Australia?',
         answers: ['Sydney', 'Melbourne', 'Canberra', 'Perth'],
         correctAnswerIndices: [2],
+        explanation: 'Canberra was chosen as the capital in 1908 as a compromise between Sydney and Melbourne.',
       ),
       Question(
         id: 'gk_2',
         prompt: 'Which planet is known as the Red Planet?',
         answers: ['Venus', 'Mars', 'Jupiter', 'Saturn'],
         correctAnswerIndices: [1],
+        explanation: 'Mars appears red due to iron oxide (rust) on its surface.',
       ),
       Question(
         id: 'gk_3',
         prompt: 'What is the largest ocean on Earth?',
         answers: ['Atlantic Ocean', 'Indian Ocean', 'Arctic Ocean', 'Pacific Ocean'],
         correctAnswerIndices: [3],
+        explanation: 'The Pacific Ocean covers about 63 million square miles and is larger than all of Earth\'s land area combined.',
       ),
       Question(
         id: 'gk_4',
@@ -203,6 +206,7 @@ class DefaultDeck {
         prompt: 'What is the capital city of Australia?',
         answers: ['Sydney', 'Melbourne', 'Canberra', 'Perth'],
         correctAnswerIndices: [2],
+        explanation: 'Canberra was chosen as the capital in 1908 as a compromise between Sydney and Melbourne.',
         consecutiveCorrect: 3,
         isKnown: true,
         priorityPoints: 0,
@@ -216,6 +220,7 @@ class DefaultDeck {
         prompt: 'Which planet is known as the Red Planet?',
         answers: ['Venus', 'Mars', 'Jupiter', 'Saturn'],
         correctAnswerIndices: [1],
+        explanation: 'Mars appears red due to iron oxide (rust) on its surface.',
         consecutiveCorrect: 3,
         isKnown: true,
         priorityPoints: 0,
@@ -227,6 +232,7 @@ class DefaultDeck {
       Question(
         id: 'gk_3',
         prompt: 'What is the largest ocean on Earth?',
+        explanation: 'The Pacific Ocean covers about 63 million square miles and is larger than all of Earth\'s land area combined.',
         answers: ['Atlantic Ocean', 'Indian Ocean', 'Arctic Ocean', 'Pacific Ocean'],
         correctAnswerIndices: [3],
         consecutiveCorrect: 3,

lib/screens/attempt_result_screen.dart

@@ -209,6 +209,22 @@ class _AttemptResultScreenState extends State<AttemptResultScreen> {
                   ),
                 );
               }),
+              if (q.explanation != null && q.explanation!.trim().isNotEmpty) ...[
+                const SizedBox(height: 16),
+                const Divider(),
+                const SizedBox(height: 8),
+                Text(
+                  'Explanation',
+                  style: Theme.of(context).textTheme.titleSmall?.copyWith(
+                    fontWeight: FontWeight.bold,
+                  ),
+                ),
+                const SizedBox(height: 4),
+                Text(
+                  q.explanation!,
+                  style: Theme.of(context).textTheme.bodyMedium,
+                ),
+              ],
             ],
           ),
         ),

lib/screens/deck_edit_screen.dart

@@ -161,6 +161,7 @@ class _DeckEditScreenState extends State<DeckEditScreen> {
     final list = questions.map((q) => {
       'id': q.id,
       'prompt': q.prompt,
+      if (q.explanation != null && q.explanation!.isNotEmpty) 'explanation': q.explanation,
       'answers': q.answers,
       'correctAnswerIndices': q.correctAnswerIndices,
     }).toList();
@@ -378,6 +379,16 @@ class _QuestionEditorCardState extends State<QuestionEditorCard> {
               ),
               maxLines: 2,
             ),
+            const SizedBox(height: 12),
+            TextField(
+              controller: widget.editor.explanationController,
+              decoration: const InputDecoration(
+                labelText: 'Explanation (optional)',
+                helperText: 'Shown when viewing question details after an attempt',
+                border: OutlineInputBorder(),
+              ),
+              maxLines: 3,
+            ),
             const SizedBox(height: 16),
 
             // Answers
@@ -474,12 +485,14 @@ class _QuestionEditorCardState extends State<QuestionEditorCard> {
 
 class QuestionEditor {
   final TextEditingController promptController;
+  final TextEditingController explanationController;
   final List<TextEditingController> answerControllers;
   Set<int> correctAnswerIndices;
   final String? originalId;
 
   QuestionEditor({
     required this.promptController,
+    required this.explanationController,
     required this.answerControllers,
     Set<int>? correctAnswerIndices,
     this.originalId,
@@ -488,6 +501,7 @@ class QuestionEditor {
   factory QuestionEditor.fromQuestion(Question question) {
     return QuestionEditor(
       promptController: TextEditingController(text: question.prompt),
+      explanationController: TextEditingController(text: question.explanation ?? ''),
       answerControllers: question.answers
           .map((answer) => TextEditingController(text: answer))
           .toList(),
@@ -499,6 +513,7 @@ class QuestionEditor {
   factory QuestionEditor.empty() {
     return QuestionEditor(
       promptController: TextEditingController(),
+      explanationController: TextEditingController(),
       answerControllers: [
         TextEditingController(),
         TextEditingController(),
@@ -521,9 +536,11 @@ class QuestionEditor {
   }
 
   Question toQuestion() {
+    final explanationText = explanationController.text.trim();
     return Question(
       id: originalId ?? DateTime.now().millisecondsSinceEpoch.toString(),
       prompt: promptController.text.trim(),
+      explanation: explanationText.isEmpty ? null : explanationText,
       answers: answerControllers.map((c) => c.text.trim()).toList(),
       correctAnswerIndices: correctAnswerIndices.toList()..sort(),
     );
@@ -531,6 +548,7 @@ class QuestionEditor {
 
   void dispose() {
     promptController.dispose();
+    explanationController.dispose();
     for (final controller in answerControllers) {
       controller.dispose();
     }

lib/screens/deck_import_screen.dart

@@ -64,6 +64,7 @@ class _DeckImportScreenState extends State<DeckImportScreen> {
         return Question(
           id: questionMap['id'] as String? ?? '',
           prompt: questionMap['prompt'] as String? ?? '',
+          explanation: questionMap['explanation'] as String?,
           answers: (questionMap['answers'] as List<dynamic>?)
                   ?.map((e) => e.toString())
                   .toList() ??
@@ -643,6 +644,7 @@ class _DeckImportScreenState extends State<DeckImportScreen> {
                       const Text('• answers: array of strings (required)'),
                       const Text('• correctAnswerIndex: number (deprecated, use correctAnswerIndices)'),
                       const Text('• correctAnswerIndices: array of numbers (for multiple correct answers)'),
+                      const Text('• explanation: string (optional, shown when viewing question details)'),
                       const Text('• isKnown: boolean (optional)'),
                       const Text('• consecutiveCorrect: number (optional)'),
                       const Text('• priorityPoints: number (optional)'),

lib/screens/flagged_questions_screen.dart

@@ -156,8 +156,10 @@ class _FlaggedQuestionsScreenState extends State<FlaggedQuestionsScreen> {
       if (id == null) continue;
       final existing = questionMap[id];
       if (existing == null) continue;
+      final explanationText = editor.explanationController.text.trim();
       final updated = existing.copyWith(
         prompt: editor.promptController.text.trim(),
+        explanation: explanationText.isEmpty ? null : explanationText,
         answers: editor.answerControllers.map((c) => c.text.trim()).toList(),
         correctAnswerIndices: editor.correctAnswerIndices.toList()..sort(),
       );
@@ -203,6 +205,7 @@ class _FlaggedQuestionsScreenState extends State<FlaggedQuestionsScreen> {
     final list = questions.map((q) => {
       'id': q.id,
       'prompt': q.prompt,
+      if (q.explanation != null && q.explanation!.isNotEmpty) 'explanation': q.explanation,
       'answers': q.answers,
       'correctAnswerIndices': q.correctAnswerIndices,
     }).toList();

lib/services/deck_storage.dart

@@ -66,6 +66,7 @@ class DeckStorage {
       'questions': deck.questions.map((q) => {
         'id': q.id,
         'prompt': q.prompt,
+        if (q.explanation != null && q.explanation!.isNotEmpty) 'explanation': q.explanation,
         'answers': q.answers,
         'correctAnswerIndices': q.correctAnswerIndices,
         'consecutiveCorrect': q.consecutiveCorrect,
@@ -133,6 +134,7 @@ class DeckStorage {
       return Question(
         id: questionMap['id'] as String? ?? '',
         prompt: questionMap['prompt'] as String? ?? '',
+        explanation: questionMap['explanation'] as String?,
         answers: (questionMap['answers'] as List<dynamic>?)
                 ?.map((e) => e.toString())
                 .toList() ??

packages/practice_engine/lib/models/question.dart

@@ -6,6 +6,9 @@ class Question {
   /// The question prompt.
   final String prompt;
 
+  /// Optional explanation shown when viewing question details (e.g. after an attempt).
+  final String? explanation;
+
   /// List of possible answers.
   final List<String> answers;
 
@@ -42,6 +45,7 @@ class Question {
   Question({
     required this.id,
     required this.prompt,
+    this.explanation,
     required this.answers,
     List<int>? correctAnswerIndices,
     @Deprecated('Use correctAnswerIndices instead') int? correctAnswerIndex,
@@ -60,6 +64,7 @@ class Question {
   Question copyWith({
     String? id,
     String? prompt,
+    String? explanation,
     List<String>? answers,
     List<int>? correctAnswerIndices,
     @Deprecated('Use correctAnswerIndices instead') int? correctAnswerIndex,
@@ -74,6 +79,7 @@ class Question {
     return Question(
       id: id ?? this.id,
       prompt: prompt ?? this.prompt,
+      explanation: explanation ?? this.explanation,
       answers: answers ?? this.answers,
       correctAnswerIndices: correctAnswerIndices ?? this.correctAnswerIndices,
       correctAnswerIndex: correctAnswerIndex ?? this.correctAnswerIndex,
@@ -119,6 +125,7 @@ class Question {
           runtimeType == other.runtimeType &&
           id == other.id &&
           prompt == other.prompt &&
+          explanation == other.explanation &&
           answers.toString() == other.answers.toString() &&
           correctAnswerIndices.toString() == other.correctAnswerIndices.toString() &&
           consecutiveCorrect == other.consecutiveCorrect &&
@@ -133,6 +140,7 @@ class Question {
   int get hashCode =>
       id.hashCode ^
       prompt.hashCode ^
+      (explanation?.hashCode ?? 0) ^
       answers.hashCode ^
       correctAnswerIndices.hashCode ^
       consecutiveCorrect.hashCode ^