11 address lines are needed to address each machine location in a 2048 X 4 memory chip.
It means that a memory of 2048 words, where each word is 4 bits. So to address 2048 (or 2K, where K means 2^10 or 1024), you need 11 bits, so 11 address lines. To express in very easy terms, without any bus-multiplexing, the number of bits required to address a memory is the number of lines (address or data) required to access that memory. Quoting from the Wikipedia article, a system with a 32-bit address bus can address 232 (4,294,967,296) memory locations.