How to Calculate the Atomic Mass of an Unknown Element M in MCl?

[transgalactic]

unknown ellement called M reacts with Cl to make MCl
0.7718 gram of MCl reacts with AgNO_3 as a result we get
2.6091 gram of AgCl.
what is the atomic mass of M
??

 

[epenguin]

You are not supposed here to ask like that, but to show enough effort to show where you got stuck or made a mistake. However I will tell you you cannot solve this with only the data in the question, you were either given or expected to be able to access other general chemical information.

You might start with the 2.6091 gram of AgCl. I guess from the formula you know what is the ratio of Ag and Cl atoms in AgCl? Can you work out the ratio of grams of Ag and Cl? For that you need information that is not written above. Maybe you can think what you need and then where to find it. From that you may start thinking about the M.