as others have said diamond is the hardest natural material and diamond nanorods are the hardest period but if you are looking for a metal it gets more complicated.
Modern high speed steels can get above a rockwell C (if you are going to try to correct me make sure to check the units, a Rockwell C of 70 is far larger then a Rockwell A of 80 for example) hardness of 70, and Osmium as what might be the hardest pure metal can be 64 or more.
Some people said Titanium and frankly that proves a great ignornace because:
a) pure titanium is very soft and not used for much of anything, like nearly all metals titanium can be greatly improved with the right additives.
b) No titanium alloy that I'm aware of can be hardened much above a Rockwell C of 50. And at that hardness Titanium is very brittle. Most titanium alloys will be used at 40 or so, so they can bend and stretch as needed for much greater impact strength.
Titanium is a good metal for many things...but it is often used for many things where it makes no sense because people just think it's cool to use the metal the space shuttle is made of.
Titanium alloys can be great for air and space craft because it won't corrode and are strong for their weight...but things like titanium razor blades and gulf heads are just silly...
The Mohs scale of hardness is not very good, it came about before any measure of absolute hardness had been invented so it was just based on what could scratch what. Things like Knoop, birnell, and the Rockwell scales are what is normally used now. The different Rockwell scales fit different ranges, with Rockwell C being the most common for measuring very hard alloys.
pgpanikkar2003, I applaud you for actually looking it up rather then just spitting out an answer but I think your book might be out of date, Tool steels have continued to advance since then.