31) the mass of an electron is approximately 1/1836
times the mass of
a) 1/1h
b) 2/1h
c) 3/1h
d) 4/2he

 is the correct choice that is option A.

Explanation:

An electron has times the mass of a proton, but an equal and opposite negative charge.

Lets is any element represented here.

Where is the number of protons as well as its atomic number.

And

is the mass number which is the number of protons and neutrons in any atom.

Note: We know that Hydrogen is devoid of neutron,so number of neutrons in a Hydrogen atom is zero.

Then

is also a representation of single proton.

So is the right choice that is option A.

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g