Sexual reproduction in $Spirogyra$ involves the fusion of:

The zygote containing $4$ meiospores in $Spirogyra$ is called

The element present in thyroxin is obtained from

Which of the following statements are applicable to brown algae?
$(I)$ They contain pigments like chlorophyll $a$,chlorophyll $c$,carotenoids,and xanthophylls.
$(II)$ They vary in color from olive green to various shades of brown.
$(III)$ Food is stored as complex carbohydrates,in the form of laminarin or mannitol.
$(IV)$ The cell wall is composed of cellulose and algin.
$(V)$ The cell wall is covered on the outside by a gelatinous coating of algin.

Select the odd one out.

Which of the following pairs consists of unicellular algae?