Single unbiased coin is tossed once. What is the probability of obtaining a head?

Introduction / Context:
An unbiased (fair) coin has equally likely faces: head (H) and tail (T). We want the probability of a head on a single toss.

Given Data / Assumptions:

• One toss of a fair coin.
• Sample space: {H, T}.
• Each outcome has probability 1/2.

Concept / Approach:
For a fair coin, symmetry implies P(H) = P(T) = 1/2. No further computation is required.

Step-by-Step Solution:
P(H) = 1/2.

Verification / Alternative check:
Long-run frequency under many tosses approaches 1/2 for heads (law of large numbers) for a fair coin.

Why Other Options Are Wrong:
1 implies certainty; 1/4 is for two successive events with probability 1/2 each; “None of these” is incorrect because 1/2 is a valid option; 0 is impossible for a fair coin.

Common Pitfalls:
Overthinking a basic fairness assumption; unless otherwise stated, “unbiased” means equal probabilities.

Final Answer:
1/2