I am baking 1kg chocolate cake and it is already in oven from 50 mins. I'm baking it at 180 degrees temperature. The cake has risen well. But the mixture is not set yet. (I did the toothpick test) I can feel it moving. I have shifted the cake to the first rack a minute before,earlier it was in the middle rack. Please suggest what's wrong?
Nothing is wrong.
Continue baking until the toothpick comes out clean. The toothpick test is more definitive than time and temperature (and temperatures are not always what they claim, but don't drastically alter yours without feedback from a RELIABLE oven thermometer..)
As I mentioned in a comment on another post, I once had a bad recipe (from a fancy book, even) that I followed with great care, making chocolate soup twice in a row by following the recipe EXACTLY. A wiser than I at the time relative pointed out that there must be a problem with the recipe, and I should just bake until it was done (per toothpick) and it made cake.
A number of factors other than "oven thermostat inaccurate" can lead to times being off - shiny .vs. dark pans, temperature of the batter at the start of cooking, altitude...
It is possible that the cake will bake to completion if you wait longer. As Ecnerwal said, it doesn't matter what the book says about time. A cake is done when it is done, and you have to test it for that. "Bake for X minutes" is rarely a good thing to do, it just gives you an initial idea of how long it may take.
But there is also a high probability that this recipe will not produce a cake. It has no eggs at all, it has very little gluten, and it has a very high amount of liquid. I don't know how much "1 tin" of condensed milk is, this varies internationally, but I guess it's anywhere from 150 to 400 ml, making your ratio of flour to liquid anything from 0.7 to 0.4. It also has almost no sugar. The little gluten from the flour is probably not enough to bind it.
It is therefore much more likely that baking will produce something pudding-like, which will stay spoon-soft forever. If you have a roast thermometer, stick it into the cake itself and measure, if it gets above 95 Celsius but doesn't set visibly within 10 minutes, then there is not much point in baking it longer. The good news is that, even if it stays soft, it will likely be edible. As long as you like the taste, you can serve it from bowls, maybe combined with fruit or topped with whipped cream.