The correct answer is (b), Sputnik 1.
Sputnik 1 was the first artificial satellite to orbit the Earth. It was launched by the Soviet Union on October 4, 1957, and it became a symbol of the Space Race between the United States and the Soviet Union.
Sputnik 1 was a small, spherical satellite that weighed about 83 kilograms. It was made of aluminum and had four external antennas. The satellite’s mission was to test the feasibility of placing a satellite in orbit and to study the upper atmosphere.
Sputnik 1 orbited the Earth for 92 days before it re-entered the atmosphere and burned up. It was a major achievement for the Soviet Union and it showed the world that the Soviets were capable of advanced space technology.
The other options are incorrect.
(a) Vostok 1 was the first human spaceflight, which was launched by the Soviet Union on April 12, 1961.
(c) Pioneer 1 was the first American spacecraft to reach the orbit of the Sun. It was launched on October 11, 1958.
(d) Soyuz 1 was the first Soviet spacecraft to dock with another spacecraft, which was launched on March 23, 1969.