1. Which of these is a useful Chemical reaction?  a) Food rancidity

b) Photosynthesis

c) Rusting

d) None

2. Which of the following statements is True?

a) Respiration is chemically the opposite of photosynthesis

b) Rusting is a rapid process

c) Complete combustion requires short supply of oxygen

d) Photosynthesis requires oxygen

Help me please, no guess work.
THANKS!.

__can be defined as which velocity changes

For a research project, a student decided to test the effect of the lead(ii) ion (pb2+) on the ability of salmon eggs to hatch. this ion was obtainable from the water‐soluble salt, lead(ii) nitrate, which the student decided to make by the following reaction. pbo(s) + 2 hno3(aq) → pb(no3)2(aq) + h2o losses of product for various reasons were expected, and a yield of 86.0% was expected. in order to have 5.00 g of product at this yield, how many grams of pbo should be reacted? (assume that sufficient nitric acid, hno3, would be used.)

One similarity and one difference between an element and a mixture of elements