In an array$-$based heap, assuming heap entries start at index $1,$ the right child of node $\backslash ($ n $\backslash )$ is at index $\_\_\_\_\_\_\_\_\_.$

Question $2$ options:

$\backslash ($ n$/2\backslash )$

$\backslash (2$n $\backslash )$

$\backslash ($ n $\backslash )$

$\backslash (2$n$+1\backslash )$