The ion that is isoelectronic with $CO$ is

The theory that can completely/properly explain the nature of bonding in $[Ni(CO)_4]$ is

The wave functions of $1s$-orbitals of two hydrogen atoms are $\psi_A$ and $\psi_B$. $\psi_A$ and $\psi_B$ are linearly combined to form two molecular orbitals ($\sigma$ and $\sigma^*$). Which of the following statements are correct?
$I$. $\sigma^*$ is equal to $(\psi_A - \psi_B)$.
$II$. In $\sigma$-orbital,one nodal plane is present in between two nuclei.
$III$. The energy of $\sigma$-orbital is lower than the energy of $\sigma^*$-orbital.

Answer the following questions:
$(i)$ Give the molecular orbitals and their types formed by $LCAO$ from $2s, 2p_{x}, 2p_{y}$ and $2p_{z}$ atomic orbitals.
$(ii)$ Provide the energy order of molecular orbitals for $Li_{2}, Be_{2}, C_{2}, N_{2}, O_{2}$ and $F_{2}$.

What is meant by the term bond order? Explain.

According to $MO$ theory,the number of species/ions from the following having identical bond order is $.........$
$CN^{-}, NO^{+}, O_{2}, O_{2}^{+}, O_{2}^{2+}$