The GATE Grind

GATE 2023 MA – Question 12

Topology · Connectedness and Compactness · 1 mark · Multiple choice

In usual ℝ³ let X={|x|+|y|+|z|∈ℚ}, Y={xyz=1}, Z={x²+y²+z²=1}, W={xyz=0}. Which statement is correct?

  1. X is homeomorphic to Y.
  2. Z is homeomorphic to W.
  3. Y is homeomorphic to W.
  4. X is not homeomorphic to W.

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Show answer and explanation

Correct answer: (D) X is not homeomorphic to W.

Explanation

W is path connected: each point connects to the origin within a coordinate plane. X is disconnected because the continuous radius map has distinct rational values, and a connected subset of ℚ is a singleton. In fact X has infinitely many connected components, whereas Y has four sign components. Z is compact and W unbounded, hence noncompact. Thus **D**.

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