The correct answer is option b, i.e., Neptune.

Introduction:
Uranus is a unique planet in our solar system, known for its tilted axis and blue-green color. It is often referred to as an "ice giant" due to its composition of water, methane, and ammonia ices. When it comes to finding a twin planet for Uranus, Neptune is considered the most similar in terms of its physical characteristics and composition.

Similarities between Uranus and Neptune:
1. Composition: Both Uranus and Neptune are classified as ice giants because a significant portion of their mass is composed of ices, including water, methane, and ammonia. These ices give them their blue-green color.
2. Size: Uranus and Neptune are similar in size, with Uranus having a diameter of about 51,118 km and Neptune having a diameter of about 49,528 km.
3. Tilted Axis: Both planets have a significantly tilted axis of rotation. Uranus is famously known for its extreme tilt of about 98 degrees, causing it to appear to roll on its side. Neptune also has a tilted axis, although not as extreme as Uranus, with an inclination of about 28 degrees.
4. Atmosphere: The atmospheres of both planets contain hydrogen, helium, and methane. Methane is responsible for the blue color of these planets.
5. Moons: Both Uranus and Neptune have a system of moons. Uranus has 27 known moons, including Miranda, Ariel, Umbriel, Titania, and Oberon. Neptune has 14 known moons, including Triton, Nereid, Proteus, and Larissa.

Differences between Uranus and Neptune:
1. Color: Uranus appears to have a blue-green color, while Neptune has a more intense blue color.
2. Internal Structure: Uranus is believed to have a solid core surrounded by a mantle of water, methane, and ammonia ices. Neptune, on the other hand, is thought to have a rocky core surrounded by a mantle of water, ammonia, and methane ices.
3. Wind Speeds: The wind speeds on Neptune are much higher than those on Uranus. Neptune has the fastest recorded winds in the solar system, reaching speeds of up to 1,200 mph (1,930 km/h).
4. Great Dark Spot: Neptune has a feature known as the Great Dark Spot, which is a large storm system similar to Jupiter's Great Red Spot. Uranus does not have a similar feature.

Conclusion:
In conclusion, Neptune is considered the twin planet of Uranus due to their similarities in composition, size, tilted axes, atmospheres, and moon systems. While there are some differences between the two planets, the similarities outweigh the dissimilarities, making Neptune the closest match to Uranus in our solar system.