In terms of electrons, What do the arrows mean?

Both 1,2−dihydronaphthalene and 1,4−dihydronaphthalene may be selectively hydrogenated to 1,2,3,4−tetrahydronaphthalene. one of these isomers has a heat of hydrogenation of 101 kj/mol (24.1 kcal/mol), and the heat of hydrogenation of the other is 113 kj/mol (27.1 kcal/mol). match the heat of hydrogenation with the appropriate dihydronaphthalene.

Which of the following shapes would represent a molecule with two bonded atoms and 3 lone pairs on only one of them , trigonal planar , bent , trigonal pyramidal , linear

How many moles of no2 will form when 3.3 moles of cu are reacted with excess hno3?