In most languages with a null reference, it is simply a memory address to a zero-length memory block. So the only memory it would occupy in these cases would be enough for a memory pointer: usually around 4 bytes.
A java.util.Date object will take about 32 bytes in memory.
2147483648 bytes
Usually four bytes.
eight bytes in most popular system
4
2
Basically 1 kilobyte
A kilobyte (or a k) is 1024 bytes, so 16k is 16*1024 bytes or 16384 bytes.
A plain integer variable in C under windows is 2 bytes in 16 bit windows, and 4 bytes in 32 bit windows.
4
It depends on the context. Each database and computer language define an "integer". In the C language an integer is defined by the hardware. It can vary from 2 to 8 bytes or more.