In multicellular animals, a group of similar cells along with intercellular substances perform a specific function. Such an organisation is called :

Tissue

The correct answer is Option (3) -Tissue

In unicellular organisms, all functions like digestion, respiration and reproduction are performed by a single cell. In the complex body of multicellular animals the same basic functions are carried out by different groups of cells in a well organised manner. The body of a simple organism like Hydra is made of different types of cells and the number of cells in each type can be in thousands.

The human body is composed of billions of cells to perform various functions. In multicellular animals, a group of similar cells alongwith intercellular substances perform a specific function. Such an organisation is called tissue. 

All complex animals consist of only four basic types of tissues. These tissues are organised in specific proportion and pattern to form an organ like stomach, lung, heart and kidney. When two or more organs perform a common function by their physical and/or chemical interaction, they together form organ system, e.g., digestive system, respiratory system, etc. Cells, tissues, organs and organ systems split up the work in a way that exhibits division of labour and contribute to the survival of the body as a whole.