According to NASA, how many Earth sized exoplanets were discovered around a single star in February 2017?

Introduction / Context:
Space science and astronomy are popular areas for general knowledge questions, especially when they involve landmark discoveries. In February 2017, NASA announced the discovery of several Earth sized exoplanets around a single ultra cool dwarf star named TRAPPIST 1. This question checks awareness of that specific numerical detail, which is often highlighted in current affairs related to space exploration.

Given Data / Assumptions:

The discovery was announced by NASA in February 2017.
The exoplanets are described as Earth sized and orbiting a single star.
We need the exact count of these planets.
Four numerical options (14, 7, 6, 11) are provided.

Concept / Approach:
The core concept is factual recall of an important scientific announcement. The TRAPPIST 1 system became famous because seven Earth sized planets were found orbiting one star, with several lying in the habitable zone where liquid water could potentially exist. Remembering the number seven is the key to solving this question correctly. No calculations are needed; it is entirely based on awareness of scientific news.

Step-by-Step Solution:
Step 1: Identify that the question refers to the TRAPPIST 1 discovery made public by NASA in 2017. Step 2: Recall that this system was notable for having seven Earth sized exoplanets around one star. Step 3: Match this remembered number with the available options and choose 7.

Verification / Alternative check:
This information can be verified from NASA press releases, reputable science magazines, and educational websites that covered the TRAPPIST 1 discovery. All of them report that seven exoplanets, similar in size to Earth, were detected in that system. Multiple reliable sources agreeing on this figure confirm that the answer is correct.

Why Other Options Are Wrong:
Option A, 14, is much higher than the well publicised number and does not match the TRAPPIST 1 system data.
Option C, 6, is close but inaccurate and may be chosen by candidates who remember the discovery roughly but not precisely.
Option D, 11, has no direct connection with this particular NASA announcement and is therefore incorrect.

Common Pitfalls:
Candidates sometimes confuse the total number of exoplanets discovered by all missions with those discovered in a single system. Another pitfall is misremembering seven as six or another nearby number due to incomplete revision. Focusing on the uniqueness of the TRAPPIST 1 system as having seven Earth sized planets helps prevent such errors.

Final Answer:
NASA reported discovering 7 Earth sized exoplanets around a single star in February 2017.