Select the option that can be used as a one-word substitute for the given group of words. An instrument for viewing distant objects in space.

Correct — A. The definition names both the job and the target: an instrument for viewing, and objects that are distant and in space.

A telescope is built for precisely that — it gathers light or radio waves from far-off sources and brings them to a focus so they can be observed.

Everything else on the list magnifies the wrong end of the scale, records instead of views, or is not the word for an astronomical instrument → option (a).

Why the others are wrong

• (b)
  Spectrograph — A spectrograph splits incoming light by wavelength and records the spectrum. It works on light some other instrument has already gathered, so it measures rather than views.
• (c)
  Microscope — A microscope magnifies things that are very small and very close. The direction is reversed: the definition asks for distant objects, not tiny ones.
• (d)
  Binoculars — Binoculars are two small telescopes joined for use with both eyes, aimed mostly at distant objects on the ground. The words "in space" point to the astronomical instrument, and the stem asks for an instrument, singular.

Two words in the stem do all the work: distant and in space.

Distant rules out anything built for close-up work, which removes the microscope immediately. In space narrows what remains to the instrument astronomy is named for.

A telescope collects electromagnetic radiation from far-off sources and brings it to a focus. Optical telescopes do this with lenses (refracting) or mirrors (reflecting), and radio telescopes collect radio waves with a dish.

Anything that studies the light after it has been gathered — a spectrograph, for instance — is an attachment to that job, not the instrument the definition names.

Key facts

• A telescope gathers light or radio waves from distant objects and brings them to a focus.
• Refracting telescopes use lenses and reflecting telescopes use mirrors.
• A microscope magnifies small objects that are close by, the opposite use from a telescope.
• A spectrograph disperses light into a spectrum and records it.

Common traps

• Choosing binoculars because they are also used to see far away
• Reading spectrograph as a viewing instrument because it works on starlight
• Answering from the word instrument alone without using "in space"

No directly related past PYQ was found.