Q.Give the IUPAC name and describe the hybridisation, bond angle and bond length at the triple-bonded carbons of $\text{CH}_3\text{CH}_2\text{C}{\equiv}\text{CH}$.

The four-carbon chain with the triple bond starting at C1 is numbered to give the triple bond the lowest locant, so the compound is but-1-yne. At each of the two triple-bonded carbons, one $s$ and one $p$ orbital combine into two collinear $sp$ hybrid orbitals at exactly $180°$ to each other; one $sp$ orbital on each carbon forms the $\text{C--C}$ sigma bond (head-on overlap with the other carbon's $sp$ orbital), and the other $sp$ orbital on the terminal carbon forms a sigma bond to its hydrogen -- so the terminal $\equiv\text{C--H}$ unit is perfectly linear, $180°$. The two remaining, mutually perpendicular $p$ orbitals on each carbon overlap sideways with the corresponding $p$ orbitals on the other carbon to form two pi bonds in two perpendicular planes, giving the triple bond overall one sigma plus two pi bonds. This is bot …

Number the chain to give the triple bond the lowest locant for the name; count sigma-bonded groups at each triple-bonded carbon (2, here) to identify $sp$ hybridisation, wh …

Numbering from the wrong end and calling it but-3-yne instead of but-1-yne (the LOWER locant must be chosen); confusing bond length trend (triple $<$ double $<$ single) with bond STRENGTH per pi bond (each individu …