The Aravalli Range is one of the oldest mountain ranges in India, stretching across multiple states and a Union Territory. It is known for its scenic beauty, rich flora and fauna, and historical significance. Let us explore the states and Union Territory through which the Aravalli Range spreads:

1. Rajasthan:
The Aravalli Range is primarily located in the state of Rajasthan. It extends from the southern part of the state, near the Gujarat border, to the northeastern regions, near the Haryana and Delhi borders. The range passes through various districts of Rajasthan, including Udaipur, Rajsamand, Bhilwara, Ajmer, Alwar, and Sirohi.

2. Haryana:
A small portion of the Aravalli Range extends into the southern parts of Haryana. It enters the state near Faridabad and continues towards the southwest, covering areas such as Gurgaon and Mewat districts.

3. Delhi:
The Aravalli Range also makes its presence felt in the National Capital Territory of Delhi. It enters Delhi from the southern part of the city near Tughlakabad and stretches towards the north, touching areas like Vasant Kunj and Mehrauli.

4. Gujarat:
Though a relatively smaller portion, the Aravalli Range spreads into the southernmost part of Gujarat. It enters the state near the Sabarkantha district and continues towards the southeast, covering parts of the Panchmahal district.

Therefore, the Aravalli Range spreads to a total of four states and one Union Territory in India. These are Rajasthan, Haryana, Delhi, and Gujarat. Hence, the correct answer is option 'a) 4'.