The mass number is the summation of number of proton and neutron present in a nucleus of an atom. For the neutral atom the number of positive charge (number of proton) must be equal to the number of electrons. The number of electrons present in an atom is the atomic number of the atom. The standard way to express the mass number (a) and atomic number (m) of a atom (say X) is
. Now for silicon number of electron or atomic number is 14. And the mass number (a) given 29. Thus the expression nucleus of silicon will be 
Answer:
The mass of the melted chocolate is 8 grams.
Explanation:
When something is melted including chocolate the mass remain the same or does not change, it is only the motion of the particles that changes and this is called law of conservation of mass.
The law states that mass can neither be created nor destroyed during chemical reaction but it remain the same.
Answer: b). The B−A−B angles between neighboring B atoms are 90∘.
Explanation: The square planar geometry is the geometry in which the four groups are connected through an angle of 90∘ and all 5 atoms are in one plane.
It is not necessary for the molecule to have two non bonding pair of electrons on atom A but if it does have , then its parent geometry will be distorted octahedral. And if it doesn't have this non bonding pair of electrons then the geometry would be the square planar.
Thus the molecule has four electron domains about the central atom A if the parent geometry is square planar otherwise it would have 8 electron domain in distorted octahedral geometry.