Due to thermal expansion with rise in temperature:

True value = scale reading $\left[1+\alpha \left({\theta }^{\text{'}}-\theta \right)\right]$

$a.If{\theta }^{\text{'}}>\theta ,$ then Scale reading <true value

$b.\Delta t=\frac{1}{2}\alpha \Delta \theta t$            

If  ${\theta }^{\text{'}}>\theta or\Delta \theta$is positive, i.e., clock will lose time, i.e., will become slow. Hence, not correct.

c. With rise in temperature, upthrust decreases. As weight remains same, hence, a floating body sinks a little more.  d. As upthrust on the body decrease with rise in temperature, hence weight of a body in a liquid $\left(=W_0-th\right)$ increase.