Which one of the following is a spacecraft?

Cassini is the correct answer (option 2). Cassini–Huygens was a robotic space probe/spacecraft sent to study Saturn and its moons and is a dedicated interplanetary spacecraft. Apophis is a near‑Earth asteroid, not a man‑made vehicle [1]. Spitzer is an infrared space telescope — a space‑based observatory rather than an interplanetary probe [2]. TecSAR (TechSar) refers to the TECSAR earth‑observation radar imaging satellite launched by PSLV, i.e., an orbiting satellite/platform rather than a deep‑space probe [3]. Thus, of the four choices, Cassini is the spacecraft (an interplanetary space probe) built and operated for exploration missions.

Sources

1. [1] https://www.sciencedirect.com/science/article/pii/S2214552425001488
2. [2] https://en.wikipedia.org/wiki/List_of_European_Space_Agency_programmes_and_missions
3. [3] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 12: Transport, Communications and Trade > Major Events > p. 57