The horizontal rows in the periodic table are called: MCQ with Answer and Explanation

Explanation:
BF3 has a trigonal planar geometry with bond angles of 120 degrees. The three B-F bond dipoles are equal in magnitude and symmetrically arranged, so their vector sum cancels out completely, resulting in a net dipole moment of zero. H2S is bent, NF3 is pyramidal, and ClF3 is T-shaped.

Explanation:
Bakelite (phenol-formaldehyde resin) is thermosetting; once molded, it cannot be reshaped by heating. Polythene, nylon, PVC are thermoplastics, which can be repeatedly softened by heat.

Explanation:
Cobalt-60 emits gamma rays used in radiotherapy to destroy cancerous cells. Carbon-12 and sodium-23 are stable. Phosphorus-32 is radioactive but used as tracer, not for cancer therapy.