Finding number of Anions given grams

[KTiaam]

Homework Statement

How many anions are there in 1.50 g of MgBr₂

Homework Equations

The Attempt at a Solution

1.5 g MgBr₂ x (1 mol MgBR₂/184.3 g MgBr₂) x (6.022 x 10²³ anions/mol)

which gave me answer of 4.91 x 10²¹

the correct answer is 9.81 x 10²¹

am i missing a step, or do i have to create a balanced equations? and use a mol to mol ratio?

any help is greatly appreciated.

 

[Bystander]

How many moles of Mg²⁺? How many moles of Br^-?