Will my graphics card work in all PCIe slots?

PCIe 16x card in PCIe 4x slot? can you put pcie 4x in 16x slot I have one in a 4x and another in a 16x, same performance from either card in the motherboard in my signature below Previously I had one Quad in a 1x slot on candyfinity slot Thanks everyone It worked just fine to use the 4x slot B

can you put ddr3 in a ddr4 slot And the thing which I love most about the PCIe is that you can use any PCIe Card on any PCIe Slot, that means you can use easily use any PCIe