A neonate has central cyanosis and short systolic murmur on the 2nd day of birth. The diagnosis is –
Tetralogy of Fallot's
Transposition of great vessels
Atrial septal defect
Ventricular Septal defect
Out of the four options, only 1st two are cyanotic heart disease i.e. TOF & TGV.
TOF can be ruled out as it does not cause cyanosis at birth.

Nelson says - "Often cyanosis is not present of birth, but with increasing hypertrophy of the right ventricular
infiindibulum and patient growth, Cyanosis occurs later in the 1st year of life."

Short systolic murmur is not of much help in reaching the diagnosis as it is present in both the conditions. Transposition of great vessels 
Transposition of great vessels is defined as : -

i) Aorta arising from right ventricle.
ii)Pulmonary artery arising from the left ventricle.

Anatomically TGA is divided into :-

A) Complete variety

Right atrium is connected to right ventricle and right ventricle is connected to aorta.
Left atrium is connected to left ventricle and left ventricle is connected to pulmonary artery.
This results in complete separation of systemic and pulmonary circulation : -