From the perspective of molecular orbital theory, which statement is false?

1. Be2 is not a stable molecule.

2. He2 is not stable but He2+ is expected to exist.

3. Bond strength of N2 is maximum amongst the homonuclear diatomic molecules belonging to the second period.

4. The order of energies of molecular orbitals in N2 molecule is: 

σ2s<σ2s*<σ2pz<(π2pxπ2py)
<(π2px*π2py*)<σ2pz*

HINT: Bond order = 12[Nb - Na]
Explanation:
Step 1:
Existence of molecule, bonding nature and energy order of molecular orbitals can be explained on the basis of molecular orbital theory as follows:
(i) Molecules having zero bond order never exists while molecular having non-zero bond order is either exists or expected to exist.
(ii) Higher the value of bond order, higher will be its bond strength. Electrons present in bonding molecular orbital are known as bonding electrons (Nb) and electrons present on anti-bonding molecular orbital are known as anti-bonding electrons (Na) and half of their difference is known as bond order i.e.,
Step 2: 
Molecular orbital diagram of given molecule and ion is as follows:
(a) Be2 (4+4=8)=σ1s2, σ1s2*, σ2s2, σ2s2*
Bond order (BO)=12[Number of bonding electrons (Nb)-Number of anti bonding electrons Na]
=4-42=0
Here, bond order of Be2 is zero. Thus, it does not exist.
(b) He2 (2+2=4)=σ1s2, σ1s2*
BO=2-22=0
Here, bond order of Be2 is zero. Hence, it does not exist.
He2+ (2+2-1=3)=σ1s2, σ1s1*
BO=2-12=0.5
Since, the bond order is not zero, this molecule is expected to exist.
(c) N2 (7+7=14)=σ1s2, σ1s2*, σ2s2, σ2s2*, π2px2π2py2, σ2pz2
BO=10-42=3
Thus, dinitrogen (N2) molecule contain triple bond and no any molecule of second period have more than double bond. Hence, bond strength of N2 is maximum amongst the homonuclear diatomic molecules belonging to the second period.
(d) It is incorrect. The correct order of energies of molecular orbitals in N2 molecule is
σ2s<σ2s*<(π2pxπ2py)<σ2pz<(π2px*π2py*)<σ2pz*