how to add a key in a react element

1    var lists = this.state.lists.map(function(list, index) {
2        return(
3            <div key={index}>
4                <div key={list.name} id={list.name}>
5                    <h2 key={"header"+list.name}>{list.name}</h2>
6                    <ListForm update={lst.updateSaved} name={list.name}/>
7                </div>
8            </div>
9        )
10    });
11