1. Element X has a mass of 300g and a ½ life of 10 years. How many grams will remain after 40 years? Hint: first determine how many ½ lives there are in 40 years

The amount of element X remain after 40 years is 18.75 grams

Explanation:

We are given:

Total time period = 40 years

One half life = 10 years

Calculating the number of half lives,

To calculate the amount of element X after 4 half lives, we use the equation:

where,

a = amount of X after n-half lives

= initial amount of X = 300 g

n = number of half lives = 4

Putting values in above equation, we get:

Hence, the amount of element X remain after 40 years is 18.75 grams

it is stable as it is in group 0 which have full outer shells of electrons

answer carbon and three oxygen atoms;