What is the most accurate way to see acidity or alkalinity

Asample of radium-226 will decay 1/4 of its original amount after 3200years. what is the half-life of radium-226?

Harvey kept a balloon with a volume of 348 milliliters at 25.0˚c inside a freezer for a night.  when he took it out, its new volume was 322 milliliters, but its pressure was the same.  if the final temperature of the balloon is the same as the freezer’s, what is the temperature of the freezer? the temperature of the freezer is  kelvins.

This is a characteristic of the elements in the periodic table that shows a pattern. it may increase or decrease across or down the table.