Analysis:
To find the odd one out, we need to identify the common characteristics or properties of four of the given options and determine which option does not possess those properties.

Options:
a) Tapir
b) Shrew
c) Ibex
d) Gazel
e) Sheep

Group Formation:
To determine the group formation, let's analyze the characteristics of each option:

Tapir: It is a large, herbivorous mammal with a short, prehensile snout, similar to a pig's snout. Tapirs are known for their distinct appearance and are native to Central and South America, as well as Southeast Asia.

Shrew: Shrews are small, insectivorous mammals with long, pointed snouts. They are known for their high metabolic rate and voracious appetite. Shrews are found throughout the world, inhabiting a variety of habitats.

Ibex: Ibex refers to several species of wild goats, typically characterized by large, curved horns. They are adapted to living in mountainous regions and are known for their agility and surefootedness.

Gazel: Gazelles are small to medium-sized antelopes known for their slender build and graceful movements. They are found primarily in Africa and parts of Asia. Gazelles are known for their speed and agility.

Sheep: Sheep are domesticated ruminant mammals, commonly kept for their wool, meat, and milk. They are herbivores and are found worldwide, particularly in agricultural settings.

Group Formation:
From the analysis of the given options, we can observe the following group formation:

- Tapir: Large, herbivorous mammal with a short, prehensile snout.
- Shrew: Small, insectivorous mammal with a long, pointed snout.
- Ibex: Wild goat species characterized by large, curved horns.
- Sheep: Domesticated ruminant mammal commonly kept for wool, meat, and milk.

Odd One Out:
The odd one out is Gazel. It does not possess the characteristic of being a mammal with a specific snout or horn structure. Gazelles are antelopes known for their slender build and graceful movements, which sets them apart from the other options in terms of physical characteristics.

Hence, the correct answer is option D) Gazel.