Correct

合不拢嘴

/ hé bù lǒng zuǐ / 
Strokes
https://i.cchatty2.com/filters:format(webp)/fit-in/684x0/img/202102/合不拢嘴-Chinese-idioms-Cchatty-b135e22a-65d9-4d96-b1fa-bf1e5d6581a3-1612776680.jpg

Collocation

1
让人合不拢嘴
2
惊奇得合不拢嘴
3
惊异得合不拢嘴
4
笑得合不拢嘴
5
乐得合不拢嘴

Definition

合不拢嘴:

Literally means:

can not close one's mouth; be extremely happy or shocked.

Actually means:

It means that one laughs with a wide open mouth wid due to his happiness, and one's mouth also remain wide open when he or she was shocked.

合不拢嘴,因为非常高兴而笑得嘴巴都合不起来,或者因为非常惊奇而张大嘴巴,合不起来。

Example

Used as complement. (作补语)
1
Kànjiàn
看见
xǔduō
许多
rén
人
ná
拿
zhāo
着
xiānhuā
鲜花
lái
来
zhùhè
祝贺
dìdi
弟弟
kǎoqǔ
考取
dàxué
大学
  
,
māma
妈妈
xiào
笑
de
得
hébùlǒngzuǐ
合不拢嘴
  
。

Seeing many people holding flowers to congratulate their brother on his college entrance, my mother could.

2
Zhāngnà
张娜
zài
在
bǐsài
比赛
hòu
后
bèi
被
píngwéi
评为
zuìjiā
最佳
qiúyuán
球员
  
,
huáibào
怀抱
zuìjiā
最佳
qiúyuán
球员
jiǎngbēi
奖杯
de
的
tā
她
lède
乐得
hébùlǒngzuǐ
合不拢嘴
  
。

Zhang Na was named the best player after the game, holding the best player trophy, she doesn't close her mouth.

3
Tā
他
de
的
zhèxiē
这些
jīngxiǎn
惊险
zāoyù
遭遇
suīrán
虽然
dōu
都
guòqù
过去
le
了
  
,
dànshì
但是
nǐ
你
tīng
听
qilai
起来
háishi
还是
huì
会
jīngqí
惊奇
de
得
hébùlǒngzuǐ
合不拢嘴
de
的
  
。

All his adventures are over, but you still sound surprised.