Questions

Except pineapple remaining all three are types of apples.

Pineapple is what kind of apple isn't an apple.

Eukaryotic cells all have a nucleus. Eukaryotes are organisms that are multicellular, although there are some examples of single cellular eukaryotes. So eukaryotic cells can be either cell with a nucleus or a eukaryotic organism's cell.

The most important feature to judge whether it has nucleus membrane.

And for other choices, they are the common features of eukaryote and prokaryote.

Let that something be 'x'

From the given data,

x + x/5 = 21

5x + x/5 = 21

6x = 21 x 5

=> x = 17.5

Hence, that something is x = 17.5.

A Libraury. It has more number of story books in it to read.

Wild goats and snow leopards are found in Himalayan region. 

Number of spectral lines from a state n to ground state is

                   n(n-1)/2 = 6