Answer:
397 g
Step-by-step explanation:
From the information given in the question , 
the atomic mass of X = 12 ,
and , the atomic mass of Y = 1 .
For the molecular formula , X₇Y₁₁ , the molecular mass is given as -
 X₇Y₁₁ = 7 * atomic mass of X + 11 * atomic mass of Y
 = 7 * 12 + 11 * 1 
 = 84 + 11 = 95 g / mol
Hence , molecular mass of X₇Y₁₁ = 95 g / mol .
Moles is denoted by given mass divided by the molecular mass , 
Hence , 
n = w / m 
n = moles , 
w = given mass , 
m = molecular mass . 
From question , 
moles n = 4.18 mol
and , 
m = molecular mass of X₇Y₁₁ = 95 g / mol .
To find the mass of the compound X₇Y₁₁ , the above formula can be used , and putting the respective values ,
 n = w / m 
4.18 = w / 95 
w = 4.18 * 95 = 397 g