Site of amino acid attachment to tRNA:

• The penultimate cytosine nucleotides in the CCA-3' terminal sequence assist proper positioning but do not form an ester linkage with the amino acid.
• During charging catalyzed by aminoacyl-tRNA synthetase, the activated amino acid forms a high-energy ester bond with the $2'$ or $3'$ hydroxyl (-OH) group of the terminal adenosine residue of the -CCA sequence at the $3'$ end of the acceptor stem.
• Pseudouridine is a modified base present in the $\text{T}\psi\text{C}$ loop, not the acceptor site.
• Dihydrouridine is located within the D loop.

Sequential order of IF3 involvement during translation initiation:

• Step 1: IF3 first binds the 30S subunit to facilitate dissociation of the recycled 70S ribosome into free 30S and 50S subunits (event A).
• Step 2: Bound IF3 prevents premature 50S reassociation and assists the 30S pre-initiation complex in positioning accurately onto mRNA via the Shine-Dalgarno sequence (event C).
• Step 3: Following proper anticodon-codon pairing of fMet-tRNA at the P site, IF3 dissociates from the 30S subunit, allowing 50S subunit docking to assemble the complete 70S initiation complex (event B).
• Thus, the precise sequential order is (A), (C), (B), corresponding to option 2.

Universality of genetic code and mitochondrial exceptions:

• Assertion (A) is true: The genetic code is nearly universal, but not completely absolute, because deviations occur in mitochondria and certain protozoans.
• Reason (R) is true: In mammalian and vertebrate mitochondria, the codon UGA, which serves as a stop signal in the standard code, specifies Tryptophan (Trp).
• Reason (R) directly explains Assertion (A) by providing empirical proof of codon reassignment that breaks strict universality.
• Therefore, both (A) and (R) are true and (R) is the correct explanation of (A).