sikdangeun icheunge isseoyo.

은 is a topic marker, signaling “as for the restaurant.” It frames 식당 as what we’re talking about. If you used 이, that would mark 식당 purely as the subject.

• 식당은 이층에 있어요 = “As for the restaurant, it’s on the second floor.”
• 식당이 이층에 있어요 = “The restaurant (subject) is on the second floor.”

Yes. Grammatically it’s correct. The nuance shifts slightly:

• With 은, you contrast or focus on “the restaurant” among other things.
• With 이, you simply state the restaurant’s location without that topic emphasis.

Floor numbers use Sino-Korean numerals (일, 이, 삼, …), not native Korean (하나, 둘, 셋, …). So:

• 1st floor = 일층 (often written 1층)
• 2nd floor = 이층 (often 2층)
  Native numbers are never used for floors.

In Korean buildings:

• 1층 = ground floor (same as “first floor” in American English)
• 2층 (이층) = one level above ground
  Basements are called 지하 1층, 지하 2층, etc.

• 에 marks a location where something exists or is found.
• 에서 marks where an action happens.
  Since 있다 here means “to exist,” we pair it with 에:
  > 이층에 있어요. (“It exists on the second floor.”)

있다 has two functions:

1. “To exist” when used with a place particle (에).
2. “To have” when used with a thing.
   Here, 이층에 있어요 = “it exists/is located on the second floor.”
   If you say 시간이 있어요, it means “I have time.”

Yes. To be more formal:
> 식당은 이층에 있습니다.
-요 ending = polite (spoken)
-습니다 ending = formal polite (speeches, announcements)

Absolutely. Korean is flexible:
> 이층에 식당이 있어요.
This emphasizes location first: “On the second floor, there’s a restaurant.”

Dropping 요 makes the speech casual or informal. Use 있어 among close friends or younger people. In polite conversation with strangers or elders, keep 요: 있어요.