Introduction:
In this question, we are asked to identify which option is not a continent out of Russia, Africa, Australia, and Antarctica. We need to select the correct answer and explain it in detail.

Explanation:
The correct answer is option 'A' - Russia.

- Russia: Russia is a transcontinental country, spanning across both Eastern Europe and northern Asia. It is the largest country in the world by land area. Although a significant portion of Russia is located in Asia, it is not considered a separate continent.

- Africa: Africa is the second-largest continent in the world, covering about one-fifth of the Earth's land area. It is home to 54 countries and is known for its diverse cultures, wildlife, and natural resources.

- Australia: Australia is the smallest continent and the largest country in Oceania. It is located entirely in the Southern Hemisphere and is known for its unique wildlife, stunning landscapes, and vibrant cities.

- Antarctica: Antarctica is the southernmost continent and is almost entirely covered by ice. It is the coldest, driest, and windiest continent on Earth. Antarctica is mainly used for scientific research and is not permanently inhabited by humans.

Conclusion:
In conclusion, out of the given options, Russia is not considered a separate continent. It is a transcontinental country that spans across both Eastern Europe and northern Asia. The other options, Africa, Australia, and Antarctica, are all continents.

The seven continents are Africa, Antarctica, Asia, Australia, Europe, North America, South America. ( Listed in Alphabetical order). In this list, Russia is not here, That's why Russia is not a continent. So, The correct answer is option A.