Questions

All enzymes are proteins but all proteins are not enzymes since, enzymes are subset of proteins.

In Chennai, Tamil Nadu place India's first HIV case reported in 1986 amongst the female sex workers.

Footsteps. 

Yes, as you walk forward, you will leave the footstep behind you.

Vatican city is not the member of UNO

For neutral atoms, the periodic trends in atomic size can be described like this

Atomic size decreases when going from left to right across a period,
Atomic size increases when going from top to bottom down a group.

Let's use these trends to try and figure out which atom would have the largest radius.

If you look at elements that are located in the same group, potassium will have a larger atomic radius when compared with sodium. Likewise, bromine will have a larger atomic radius when compared with chlorine.

Now focus on potassium and bromine. Since potassium is located at the start of period 3, and bromine at the end of the same period, potassium will have a larger atomic radius than bromine, and thus the largest atomic radius of the four given atoms.