A.) half - life of a radioactive substance is defined as the time during which concentration of the substance becomes half the initial value.
It was former President Woodrow Wilson who was nominated by self-announcement and he become the president of the United States of America in the year 1913 up to the year 1921. He was the 28th president of the United States and he runs on the presidential election year 1912 and won the presidential title. He served the country for 9 years. Former President Woodrow Wilson was born is Virginia, US in 1856 and he died on the year 1924 at the age of 67.
A chemical reaction (signs)
- rusting
- change in base of chemical
- for example lets say u mix two chemicals, and then it becomes a different new chemical (it changed from the inside)
a physical
- a physical reaction is outer looks not inside.
- it changes on the outside, like changing a color
