Correct

非常 vs 极 vs 十分

/ fēicháng vs jí vs shífēn /
Strokes

Definition

非常, 极 and 十分 are all Adverbs, which means [very; extremely].

Example

非常, 极 and 十分 are all indicate a very high degree.
1) 十分 is more literary than 非常.

2) 极 is monosyllabic and so is usually followed by a monosyllabic adjective (e.g.极妙 wonderful, 极怪 very strange, 极强 extremely strong, etc.) but it can also precede a disyllabic word. 极 is also literary. Besides, 极 can be a complement.

3) In example ① all the three words are interchangeable because the style of the sentence could be either literal or colloquial.
1
Jīntiān
今天
de
tiān
天气
fēicháng
非常
  
(
shí
fēn
  
)
  
(
  
)
  

It is very hot today.

极 is better because of syllabic collocation. If 非常 or 十分 is used, it is better to use 古怪, though 非常怪, 十分怪 are also fine.
1) 极 plus 了 can be a complement, while 非常, 十分 cannot be so used;

2) With a disyllabic adjective, 极其 can be used instead.
2
de
xìng
性格
guài
极怪
  

He is very eccentric.

3
de
xìng
性格
极其
guài
古怪
  

His personality is extremely eccentric.

4
Shā
沙漠
de
tiān
天气
及其
yán
炎热
  

The weather in the desert is extremely hot.

Only 极了 can be used as the complement.
In the literary language, 非常之…… can be used in phrases like 非常之痛快. 极 and 十分 cannot be used like this.
5
li
那里
de
fēngjǐng
风景
měi
le
极了
  

The scenery there is very beautiful.

6
Zhèzhǒng
这种
diàn
电器
hǎo
yòng
le
极了
  

The electric appliance is very easy to use.

7
Jīntiān
今天
de
tiān
天气
  
,
lěng
  
,
shūfu
舒服
le
  

It is pleasing for it is neither cold nor hot today.

非常 can also mean "unusual, special". It's not an adverb, but an adjective.
8
Xiànzài
现在
shì
fēicháng
非常
shí
时期
  
,
rénmen
人们
wǎn
夜晚
néng
chūmén
出门
  

It's an extraordinary time when people can't go out at night.

9
Dǎng
zhàokāi
召开
le
cháng
fēicháng
非常
dàibiǎohuì
代表大会
  

The Party held an nonpermanent representative congress.

十分 can also mean "the whole, all". In such a case, it is not an adverb, but a phrase.
10
yòng
le
shí
fēn
de
qi
力气
cái
bāndòng
搬动
jiā
家具
  

It took him a lot of effort to move the furniture.