A and B are separated by C
But Mandarin doesn’t like to use passive, so it has a different construction for this:
A 与 B 隔着 C
This 隔 (gé) means ‘to separate’ or ‘to partition’, so literally this is something like “A from B separate C”. It’s an active sentence, not a passive one. The general structure is:
[noun A] 与 [noun B] 隔着 [barrier]
You can also use 和 instead of 与.
中国与蒙古隔着万里长城。 Zhōngguó yǔ Ménggǔ gézhe wànlǐ chángchéng. China and Mongolia are separated by the Great Wall of China.
我的家与他的隔着一条江。 Wǒ de jiā yǔ tā de gézhe yītiáo jiāng. My home is separated from his by a river.
这间教室和那间隔着一堵墙。 Zhè jiān jiàoshì yǔ nà jiàn gézhe yī dǔ qiáng. This classroom is separated from that one by a wall.
中国与美国隔着哪个大洋？ Zhōngguó yǔ měiguó gézhe nǎge dàyáng? Which ocean separates China and America?
隔着 with 之间
There is another structure for 隔着, in which you put 之间 (zhījiān) after the subject. 之间 means ‘between’ or ‘amongst’, so you end up with something like ‘in between A and B, there is the barrier of C’. The general structure is:
[noun A] 和 [noun B] 之间隔着 [barrier]
You can also use this structure to talk about barriers between a plural subject:
[plural noun] 之间隔着 [barrier]
爱情和恨意之间隔着不远的距离。 Àiqíng hé hènyì zhījiàn gézhe bù yuǎn de jùlí. Love and hate are not separated by much. _I.e. 'Love and hate are not that different._'
天才与精神错乱之间只隔着成功。 Tiāncái yǔ jīngshén cuòluàn zhījiān zhǐ gézhe chénggōng. Genius and madness are separated only by success.
广东和广西之间隔着什么？ Guǎngdōng yǔ guǎngxi zhījiàn gézhe shénme? What separates Guangdong from Guangxi?
我们之间不只隔着太平洋。 Wǒmen zhījiān bùzhǐ gézhe tàipíngyáng. We are not just separated by the Pacific Ocean.
他们之间隔着很远的距离。 Tāmen zhījiàn gézhe hěn yuǎn de jùlí. They are separated by a great distance.
There’s also a Chinese idiom that uses 隔, although not in the structure described above:
一日不见如隔三秋。 Yī rì bù jiàn rú gé sān qiū. One day apart seems like a separation of three years.