55) Number of sigma bonds in P₄O₁₀ is:

56) The values of electronegativity of atoms A and B are 1.2 and 4.0 respectively. The percentage of ionic character of A−B bond is:

57) CaO and NaCl have the same crystal structure and approximately the same ionic radii. If U is the lattice energy of NaCl, the approximate energy of NaCl is:

58) CH₃⁻ is an isostere of:

59) The nature of π bond in perchlorate ion is: