Choose a similar word ?

Kolkata, Mumbai, Mangalore

Marathon is to Race as Hibernation is to Sleep.

Marathon is a long race in the similar way Hibernation refers to a long sleep.

Here the given number analogy follows two patterns that,

6 

18 --> 6 x 3

4

12 --> 4 x 3

OR

6

18 ----> 6x6/2 = 18

4

8 ----> 4x4/2 = 8

As 12 is not available in the options, 8 is correct answer.

Here Thread and String are Synonyms of each other. Then the answer will be the synonym of Cask. 

• Cask is nothing but a large barrel-like container used for storing liquids, typically alcoholic drinks. 

Ex : Drum, Vessel, Tank, Barrel, Hogshead, Firkin,...

• Here from the options Barrel is the only synonym of Cask.

Thus,  Thread : String :: Cask : Barrel

Square is 2-dimensional 4 sided figure Whereas Cube is 3-dimensional figure which looks like Square.

Similarly, Triangle is 2-dimensional 3 sided figure Whereas Pyramid is 3-dimensional figure which looks like Triangle.

Lightning produces thunder just as a seed will eventually produce a grape.

Radiation shows the property of spreading while the rest three shows concentration at a point.

Bleak means an area of land lacking vegetation and exposed to the elements like deserts.

Meaning of Discordant = Harsh

That implies Harsh opposite is soft.