The shielding of electrons gives rise to an effective nuclear charge, z_{\rm eff}, which explains why boron is larger than oxygen. estimate the approximate z_{\rm eff} felt by a valence electron of boron and oxygen, respectively?

a. +5 and +8
b. +3 and +6
c. +5 and +6
d. +3 and +8
e. +1 and +4

B. +3 and +6

Explanation:

The values of the Z is estimated by subtracting the core electrons from the atomic number of the element.

Oxygen has an atomic number of 8, 6 valence electrons, and 2 core electrons. Therefore the value of Z = 8-2 = +6

Boron has an atomic number of 5, 3 valence electrons and 2 core electrons. Therefore, the value of Z = 5-2 = +3

65.39g of Zn will produce 22.4L of gas.

Explanation: For a reaction,

2 moles of HCl produces 1 mol of gas.

Molar Volume of gas for 1 mole at STP = 22.4 litres

As seen from the balanced chemical equation, 1 mole of Zn gives 1 mole of gas. Hence 22.4L of gas is produced.