The force holding atoms together in a covalent bond is: MCQ with Answer and Explanation

Explanation:
Complete combustion of ethanol: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + heat. In sufficient oxygen, carbon burns to CO₂, hydrogen to H₂O. Incomplete combustion (lack of O₂) produces CO and soot (C). Ethanol is a biofuel, reducing CO₂ emissions if derived from biomass. It has high octane number and is blended with petrol (gasohol). CO₂ is a greenhouse gas, but bioethanol is carbon-neutral over cycle.

Explanation:
Brass is an alloy of copper (Cu) and zinc (Zn). Proportions vary to give different properties; common brass is 70% Cu, 30% Zn. Bronze is primarily Cu and Sn (tin). Solder is Pb and Sn. Steel is Fe with C and other elements. Brass is used for musical instruments, plumbing, and decorative hardware due to its gold-like appearance and corrosion resistance.

Explanation:
The p-block includes elements from groups 13 to 18. Gallium (Group 13), Tin (Group 14), and Bismuth (Group 15) are all p-block elements. Zinc (Group 12) has a completely filled d-subshell (3d10) in its ground state and common oxidation states, placing it in the d-block.