Q4. Arrange B, C, N, F and Si in order of non-metallic character (NCERT Exercise 3.39, page 99).
F > N > C > B > Si (option (c)). Non-metallic character rises across period 2 (B < C < N < F), and silicon, below carbon and a metalloid, is the least non-metallic.
Q5. Which block, period and group does an element with outer configuration 4s2 4p3 belong to? Name it.
p-block (last electron in 4p), period 4, five outer electrons so group 15: arsenic (Z = 33), a metalloid.
Q6. What are the major differences between metals and non-metals (NCERT Exercise 3.26, page 97)?
Metals: on the left of the table; usually solid with high melting points (mercury is liquid); good conductors of heat and electricity; malleable and ductile; tend to lose electrons, forming basic oxides. Non-metals: top right; solids or gases with low melting points (boron and carbon are exceptions; bromine is liquid); poor conductors; brittle when solid; tend to gain electrons, forming acidic oxides.
Q7. Why are the lanthanoids placed in a separate row instead of in the main body of the table?
Their last electron enters the 4f subshell, and the 14 elements Ce to Lu have very similar properties. Putting them in the main table would need 14 extra columns; placing them below keeps the table’s shape and keeps similar elements together, with lanthanum in group 3.