Among the options given, the modern tank is "Option 3: Arjun." The Arjun is a contemporary main battle tank (MBT) developed by the Defence Research and Development Organisation (DRDO) of India. Here are some detailed reasons why Arjun is considered a modern tank:

1. Indigenous Design and Development: The Arjun tank is a product of indigenous design and development by DRDO, making it a symbol of technological advancement in India`s defense industry. It demonstrates the country`s capabilities in designing and manufacturing modern military equipment.

2. Advanced Firepower: The Arjun tank is equipped with a 120mm rifled gun, which is capable of firing various types of ammunition, including armor-piercing fin-stabilized discarding sabot (APFSDS), high explosive squash head (HESH), and anti-tank guided missiles (ATGMs). Its firepower allows it to engage and destroy a wide range of targets with precision.

3. Enhanced Protection: The Arjun tank incorporates advanced armor protection, including composite and modular armor, to provide improved defense against various threats. It features advanced explosive reactive armor (ERA), which can significantly reduce the effectiveness of incoming projectiles. It also has a laser warning and countermeasures system to detect and counter enemy laser threats.

4. High Mobility: The Arjun tank is powered by a 1,400 horsepower engine, providing excellent mobility across different terrains. It has a hydropneumatic suspension system that ensures enhanced cross-country mobility, enabling it to traverse rough terrain and overcome obstacles effectively.

5. Modern Technology Integration: The Arjun tank integrates modern technologies, such as digital control systems, advanced fire control systems, and night vision capabilities. It has a computerized fire control system that enables accurate targeting and engagement of enemy forces. It also incorporates a day/night thermal imaging system for enhanced situational awareness.

6. Crew Comfort and Safety: The Arjun tank focuses on crew comfort and safety. It features a climate control system, providing a comfortable environment for the crew in extreme weather conditions. The tank has a separate crew compartment, reducing the risk of casualties if the hull is hit. It also includes NBC (Nuclear, Biological, and Chemical) protection systems to safeguard the crew from hazardous environments.

7. Battle-Tested: The Arjun tank has undergone extensive testing and evaluations, including rigorous field trials and exercises, to validate its performance and combat capabilities. It has been refined and improved based on feedback from the Indian Army and has demonstrated its operational readiness and effectiveness.

It`s important to note that the other options mentioned are not tanks:

- Bhim: Bhim is a self-propelled artillery gun developed by DRDO, but it is not a tank.

- Akash: Akash is an indigenously developed surface-to-air missile system used for air defense, not a tank.

- Prithvi: Prithvi is a series of indigenously developed short-range ballistic missiles, not a tank.

Therefore, the correct answer is "Option 3: Arjun" as the modern tank.