• val name = null is of type Nothing?
• The multi line string will contain a lot of whitespace if you don't call trimMargin
• The when snippet is wrong. The branch isOdd(x) will never be triggered because it compares the value of the string x to the boolean result of the call. If you want to have method calls in the when branches, you need to pull the argument out of the when-expression.
• The correct name for "Tuples" is "Data Classes" paired with "Destructuring". Tuples are something different.
• The correct name for "Object instance" is "Constructor call"
• You can leave out the body of a class if it's empty
• The correct name for "Attributes" is "Primary Constructor"
• A better name for "Multiple Constructors" is "Optional Arguments in Constructors (as alternative to overloaded constructors)"

Take a look at the image below. As you can see there is no way of telling in which section you're in. Users might miss checking other sections if they don't realize these are navigation links.

My suggestion is to add a selected state, a line below the current section or a different background, to the current section.

There is mistake in this category. In Java section we have method createList, but called only create. In Kotlin section there is no mistake.

Screenshot