What Ionizes the Gas in a Planetary Nebula (See the Image

question 51

Multiple Choice

What ionizes the gas in a planetary nebula (see the image below) and makes it visible?

• A) X-ray photons emitted by a pulsar
• B) Ultraviolet photons emitted by a white dwarf
• C) The shock wave from a supernova
• D) Hydrogen burning in the nebular gas

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Definitions:

Quota

A limited quantity of a particular product that under official controls can be produced, exported, or imported.

Excise Tax

A tax charged on specific goods and services, such as tobacco and alcohol, often imposed to discourage their use or to generate revenue.

Sales

The exchange of a commodity for money; the action of selling something.

Quota

A limit placed on the quantity of a specific good that can be imported or exported during a given timeframe, usually to protect domestic industries.