Router is sky hub(2013). The max speed is 100mbps but my wifi adapter is a 300mbps speed at 2.4GHz. Will I achieve a 100mbps speed then? Also, my PC is on the third floor and my router is on the first floor....so will there be any interferences?
The key here is the 300mbps number is almost a outright lie....but of course that is the world or marketing.
This is like calling a gbit ethernet cable 2gbit because it can transmit 1gbit and receive 1gbit at the same time....but ethernet can actually do that.
You will likely get nowhere near 100mbps but there is no way to predict the actual rates.
This site should set more realistic expectations on what you can acheive. Be very careful to read test results correctly, on the high end 802.11ac routers the are testing to a end user device that has 4 antenna/feed which is very very rare in actual usage.