Answer : The half-life of this substance will be, 45 minutes.
Explanation :
First we have to calculate the value of rate constant.
Expression for rate law for first order kinetics is given by:

where,
k = rate constant = ?
t = time passed by the sample = 90.3 min
a = initial amount of the reactant = 400
a - x = amount left after decay process = 100
Now put all the given values in above equation, we get


Now we have to calculate the half-life of substance, we use the formula :



Therefore, the half-life of this substance will be, 45 minutes.
Answer:
The watt (symbol: W) is a unit of power. In the International System of Units (SI) it is defined as a derived unit of 1 joule per second, and is used to quantify the rate of energy transfer
Explanation:
Mechanical or Electromagnetic
In scientific notation, if the exponent of 10 is positive, the number is very very large. In the metric system, very large numbers are expressed in megameters (Mm) or gigameters (Gm). Gigameters is equal to 10⁹ meters. So, in SI prefix, that would be equal to 150 Gm. In kilometers, that would be equal to:
1.5×10¹¹ m * (1 km/1000 m) = 1.5×10⁸ km
Answer:
K. E = 6.0796 × 10^ -21 Joule
Explanation: see attachment