Questions

Secondary succession means in an ecosystem renewal of itself after all or a portion has been destroyed.

After a forest fire, the whole forest had destroyed but after that again renewal of that forest is also an example of secondary succession.

EyeROV TUNA, the India's first underwater robotic drone was launched and handed over to Kochi based DRDO lab and it can send realtime videos of ships and other underwater structures to help with their repair and maintenance.

The system unit of a personal computer typically contains microprocessor, disk controller and serial interface but it does not contain modem.

A promise. 

The Promise made to somebody by you can be break but you cannot touch it.

Tropical cyclones are also known as 'typhoons' in china, and Willy Willies in Australia.

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.