Correct

还 vs 回

/ huán vs huí /
Strokes

Formula

1
还(回)礼 (send a present in return)
2
还(回)嘴 (answer back/scold back)
3
还价 (counter-bid/counter-offer)

Definition

还 and 回 both are Verbs, which means [return; go back].

Example

还 and 回, both words mean "to return to the original place". 还 is literary and 回 is colloquial.
1) In example ① 还乡 is a literary expression, while 回到家 in example ② is colloquial.

2) 还 and 回 in these two sentences are not interchangeable.

3) 还乡 is a rare collocation, but 回国, 回校, 回家, etc. are commonly used (In literary language, 还家 is said, but quite rare now).
1
20
20
nián
méiyǒu
没有
huánxiāng
还乡
le
  

He has not returned his native place for 20 years.

2
xià
下午
6
6
diǎn
xiàbān
下班
  
,
6
6
diǎnbàn
点半
jiù
可以
huídào
回到
jiā
  

She left off work at 6 p.m,and arrived home at 6: 30p.m.

还 and 回, the two verbs also mean " to requite or repay", in this usage the two words are sometimes interchangeable, but 还 is more literary.
还(回)礼 (send a present in return) 还(回)嘴 (answer back/scold back) 还价 (counter-bid/counter-offer)
3
shuō
shénme
什么
zhè
háizi
孩子
dōu
yào
hái
  
(
huí
  
)
zuǐ
  

The child would answer back to all she said.

4
xiàng
huīshǒu
挥手
zhì
致意
  
,
xiàng
huán
还礼
  

I waved to her and she returned the salute.

还 and 回, the two words have their own usages respectively. For example, 还 means "to return sth.".
5
yào
shūguǎn
图书馆
hái
shū
  

I will go to the library to return the books.

6
qiàn
de
qián
xiàyuè
下月
可以
hái
  

I will pay back your money next month.

回 means "to reply, to refuse or to turn round"; in these usages, 还 and 回 are not interchangeable.
7
jīng
已经
gěi
huí
le
xìn
  

I have replied his letter.

8
ge
yāoqǐng
邀请
dōu
bèi
huí
le
  

He declined several invitations.

9
xiàngqián
向前
zǒu
le
yòu
huíguò
回过
tóu
lái
wàng
lewàng
了望
  

He stepped forward a little and turned back.