Q.Which of the following statements is true about dictionaries in Python ? (A) A dictionary is an example of sequence datatype. (B) A dictionary cannot have two elements with same key. (C) A dictionary cannot have two elements with same value. (D) The key and value of an element cannot be the same.

Concept: Dictionary key uniqueness — a Python dictionary is a mapping type, not a sequence, and it enforces unique keys.

1. Option (A) is false: dictionaries are mapping types, not sequences (sequences are lists, tuples, strings, etc.).
2. Option (B) is true: dictionary keys must be unique — if you assign a value to an existing key, the old value is overwritten.
3. Option (C) is false: values can repeat freely (e.g., {'a': 1, 'b': 1} is valid). …

The Concept: What a Dictionary Actually Is

A Python dictionary is a mapping type — it stores key-value pairs, where each key is used to look up its associated value. This is fundamentally different from a sequence (like a list, tuple, or string), which stores items in a positional order. Sequences are indexed by integers; dictionaries are indexed by their keys.

The core rules are:

• Keys must be unique — you cannot have two entries with the same key.
• Keys must be immutable (strings, numbers, tuples of immutables).
• Values have no restrictions — they can be any object, and they can repeat freely.
• There is no rule that a key and its value must be different.

Now let’s test each statement against these rules.

Step-by-Step Analysis

1. Statement (A): “A dictionary is an example of sequence datatype.”

A sequence is an ordered collection where elements are accessed by their position (index). Lists, tuples, and strings are sequences. A dictionary is unordered (in Python <3.7) or insertion-ordered (Python ≥3.7), but it is not accessed by integer index — it is accessed by key. It belongs to the mapping category, not sequence.

Therefore, (A) is false.

2. Statement (B): “A dictionary cannot have two elements with the same key.”

This is the defining rule of dictionaries. If you try to assign a value to an existing key, the old value is overwritten — you never get two entries with the same key. For example:

d = {'a': 1, 'a': 2}   # This results in {'a': 2}, not two 'a' entries

The language enforces key uniqueness. So (B) is true. …