Answer:
C) Covalent bonds come about because of a sharing of electrons; ionic bonds do not.
Explanation:
There are two main types of chemical bonds- covalent and ionic/electrovalent bonds.
Ionic bond: Ionic or electrovalent bonds are characterized by the transfer of electrons from electropositive atoms (metals) to electronegative atoms (non-metals). The metal atoms after donating their electrons become positively charged ions (cations) while the non-metal atoms after accepting electrons become negatively charged ions (anions). Strong electrostatic forces of attraction constitutes ionic bonds.
Covalent bond: Covalent bonds are formed by the sharing of electrons by the atoms involved in the bond; usually between atoms of comparable electronegativities or atoms of the same element. The shared electrons are contributed by each of the atoms involved in the bonding or may be contributed by only one of the atoms. In covalent bonding, molecules rather than ions are formed.
Answer:
C
Explanation:
Rust is a chemical change (reaction) all of the other options only change the state meaning that it is a physical reaction.
Answer:
102.807 kPa
Explanation:
There are some assumptions to be made in the answer. The air inside the balloon acts as an ideal gas at a given temperature conditions.
Using the combined ideal gas equation.
P= absolute pressure of air inside the balloon.
V= volume of air inside the balloon (6.23 L= 6.23 * 10⁻³ m³)
n= moles of gas(air). (0.250 mol)
R= Universal gas constant ( 8.314 J / mol·K)
T= Temperature in Kelvin
T= 35 + 273.15 = 308.15 K
So, 
P= 102.807 * 10³ Pa
P= 102.807 kPa
Answer: Objects with like charge repel each other.
Anything which changes the composition of starting material is a chemical property or chemical change. For example: you bake cake or cook food the heat changes composition of these. So cooking is a chemical change.
But evaporation of water is a physical change because even after evaporating it is still water molecules not changed to something else.
Combustion of any substance is burning of any substance in air. Combustion is actually the burning of a substance with oxygen in air. So, when a substance undergoes combustion it changes in it’s composition.
COMBUSTION IS A CHEMICAL CHANGE
