Explain optionals in Swift with examples.

Optionals represent values that might be absent. Declaration: var name: String? = nil. Unwrapping methods: 1) Force unwrapping: name! (crashes if nil), 2) Optional binding: if let safeName = name { }, 3) Nil coalescing: name ?? "Default", 4) Optional chaining: person?.address?.street. Optionals prevent runtime crashes by making nil handling explicit and safe.