The correct option is (a).
Explanation
The rise of Magadha as the most powerful Mahajanapada was driven by the ambitious expansionist policies of its rulers, particularly those of the Haryanka dynasty, and its strategic geographical advantages.
Statement 1 is Correct:
Bimbisara and his son Ajatasattu were the earliest major rulers of the Magadha empire (Haryanka Dynasty) who adopted aggressive policies to expand their territory. Bimbisara used a combination of matrimonial alliances (with Kosala, Vaishali, and Madra) and conquest (annexation of Anga). Ajatasattu followed a more aggressive policy of war, conquering the Vajjis (Lichchhavis) and Kosala. Thus, they employed all possible means-diplomacy, marriage alliances, and military conquest-to expand their janapada.
Statement 2 is Correct:
Rajagriha (modern Rajgir) was the initial capital of Magadha. It was a strategic location surrounded by five hills, making it impregnable. Later, the capital was shifted to Pataliputra (modern Patna) because of its central location and proximity to the river Ganga, which facilitated trade and military movement. This shift is historically attributed to Udayin, the successor of Ajatasattu.
Statement 3 is Incorrect:
Alexander the Great invaded the northwestern part of the Indian subcontinent around 326 BCE. However, he did not conquer Magadha. His army refused to march further east beyond the river Beas (Hyphasis), partly due to exhaustion and partly out of fear of the massive army of the Nanda dynasty, which was ruling Magadha at that time. Alexander was forced to retreat without ever engaging the Magadhan forces.
Key Takeaway:
Magadha's supremacy was established through the ruthless expansionist strategies of Bimbisara and Ajatasattu and the strategic relocation of the capital to Pataliputra. Alexander's invasion was confined to the North-West and did not extend to the Magadhan empire in the Gangetic plains.