Among V(CO)6, Cr(CO)5, Mn(CO)5, Fe(CO)5, [Co(CO)3] 3 , [Cr(CO)4] 4 and Ir(CO)3, the total number of species isoelectronic with Ni(CO)4 is _______________. [Given, atomic number: V = 23, Cr = 24, Mn = 25, Fe = 26, Co = 27, Ni = 28, Cu = 29, Ir = 77] ( IIT Ad 2024 Paper-1)

Complete reaction of acetaldehyde with excess formaldehyde, upon heating with conc. NaOH solution, gives P and Q. Compound P does not give Tollen’s test, whereas Q on acidification gives positive Tollen’s test. Treatment of P with excess cyclohexanone in the presence of catalytic amount of p-tolunesulfonic acid (PTSA) gives product R. Sum of the number of methylene groups (-CH2-) and oxygen atoms in R is ________(IITAd 2024 Paper-1).